System and method of driving ultrasonic transducers
A transducer is optimally driven at or near its resonant frequency by a driver system that adapts to variations and/or changes to the resonant frequency of the transducer due to variations in piezo materials, manufacturing, assembly, component tolerances, and/or operational conditions. The system may include an output controller, a phase track controller, a frequency generator, a drive, circuitry to determine a phase angle between the transducer voltage and transducer current, and circuitry to obtain transducer admittance from the transducer voltage and transducer current.
1. A system for driving an ultrasonic transducer, the system comprising:
a controller adapted to provide a voltage and a frequency, the controller configured to vary the voltage based on a current error signal derived from a drive current through a transducer and from a current command, the controller configured to vary the frequency based on at least one parameter indicative of whether the transducer is at or near a resonance state; and
a drive adapted to receive the voltage and the frequency from the controller, and adapted to provide a drive voltage at a drive frequency to the transducer based on the voltage and the frequency received from the controller, the drive voltage being at a level that maintains the drive current at substantially the current command, the drive frequency being at substantially a resonant frequency of the transducer,
wherein the at least one parameter includes a phase angle between the drive current and the drive voltage.
2. The system of claim 1 , wherein the at least one parameter further includes admittance of the transducer.
3. The system of claim 1 , wherein the controller includes a current controller configured to vary the voltage based on the current error signal, a frequency controller configured to vary the frequency based on the at least one parameter, and a controller scheduler configured to alternate operation of the current controller and the frequency controller.
4. The system of claim 3 , further comprising a sense circuit configured to provide a measure of the drive current and to generate and provide to the frequency controller a measure of admittance of the transducer and the at least one parameter.
5. The system of claim 3 , wherein the frequency controller is configured to execute a frequency scan that finds a frequency that is at or near the resonant frequency of the transducer and to set the drive frequency to the frequency that is found.
6. The system of claim 3 , wherein the frequency controller includes a frequency tracker configured to execute a frequency track function that adjusts the drive frequency to compensate for a fluctuation in the resonant frequency.
7. The system of claim 6 , further comprising a frequency generator, wherein the frequency tracker includes a peak detector and a frequency stepper commanded by the peak detector to determine a first frequency step, the first frequency step having random step size between a predetermined frequency range and having a random step direction being either up or down, the frequency stepper configured to provide the frequency step to the frequency generator which generates a new frequency based on the frequency step, the frequency generator configured to provide the new frequency to the drive;
wherein when admittance of the transducer increases by an amount greater than a predetermined amount as a result of the new frequency, the frequency stepper determines a next frequency step having the same step direction as the first frequency step and having a step size based on the amount of admittance increase; and
wherein when admittance of the transducer decreases by an amount greater than the predetermined amount as a result of the new frequency, the frequency stepper determines a next frequency step having the opposite step direction as the first frequency step and having a step size based on the amount of admittance decrease.
8. The system of claim 6 , further comprising a frequency generator;
wherein the frequency tracker includes a feedback controller configured to receive a phase angle error term as input and to output a frequency step having a magnitude and a direction that drive the phase angle error term toward zero, the phase angle error being a difference between a command phase term and the phase angle; and
wherein the frequency generator is configured to generate a new frequency based on the frequency step and to provide the new frequency to the drive.
9. The system of claim 1 , wherein the controller includes a feedback controller configured to receive the current error signal as input and to output a voltage that drives the current error signal to zero, the current error signal being a difference between the current command and the drive current; and
wherein the drive is configured to generate the drive voltage by amplifying the output voltage.
10. The system of claim 1 , wherein the drive includes a switching amplifier.
11. The system of claim 10 , wherein the switching amplifier includes an output filter, the output filter including a pair of in-phase magnetically coupled inductors.
12. The system of claim 11 , wherein the switching amplifier is a dual channel amplifier configured to deliver two differential outputs in which output of a first channel and output of a second channel are phase shifted from each other by 180 degrees.
13. The system of claim 12 , wherein the in-phase magnetically coupled inductors are configured to double the frequency and decrease the amplitude of current ripple in each of the in-phase magnetically coupled inductors.
14. The system of claim 1 , wherein the controller and drive are coupled to an apparatus containing the transducer, the apparatus selected from the group consisting of a surgical device, a cutting tool, a fragmentation tool, an ablation tool, and an ultrasound imaging device.
15. A method for driving an ultrasonic transducer, the method comprising:
providing a drive voltage at a drive frequency to a transducer, the drive voltage causing a drive current through the transducer;
sensing the drive current;
determining a current error from the sensed drive current and from a current command;
adjusting the drive voltage based on the current error;
determining at least one parameter from the sensed drive current and from the voltage level, the at least one parameter indicative of whether the transducer is at or near a resonance state, the at least one parameter including a phase angle between the drive current and the drive voltage;
adjusting the drive frequency based on the at least one parameter, including maintaining the drive frequency at or substantially at a resonant frequency of the transducer.
16. The method of claim 15 , wherein the adjusting of the drive frequency includes applying a phase error term to a proportional-derivative controller, the phase error term being a difference between a command phase term and the phase angle between the drive current and the drive voltage.
17. The method of claim 15 , wherein the providing of the drive voltage at the drive frequency to the transducer includes filtering differential outputs of a dual channel switching amplifier, the filtering performed at least in part by using a pair of in-phase magnetically coupled inductors.
18. The method of claim 17 , wherein the filtering includes phase shifting by 180 degrees output of a first channel of the switching amplifier from output of a second channel of the switching amplifier.
19. The method of claim 18 , wherein the filtering further includes simultaneously doubling the frequency and decreasing the amplitude of current ripple in each of the in-phase magnetically coupled inductors.
20. The method of claim 15 , wherein the transducer is contained in an apparatus selected from the group consisting of a surgical device, a cutting tool, a fragmentation tool, an ablation tool, and an ultrasound imaging device.