Ultrasonic Transducer Resonance Tracking via Phase-Shift Control
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Solution Overview
Problem
Existing methods for controlling ultrasonic transducers in electrosurgical instruments face challenges in accurately identifying and maintaining the mechanical resonance frequency, especially due to variations caused by mechanical load and tissue contact.
Innovation Solution
A method that calculates signal coefficients for both the current and voltage signals to determine the transducer phase shift, allowing for adjustments to the signal frequency to match the mechanical resonance frequency. This method uses a feedback control loop and does not require zero-crossing detection or low-pass filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If zero-crossing detection is used to determine phase shift, then the phase shift measurement can be obtained, but the measurement becomes very sensitive to noise requiring careful low-pass filtering
Solution Approach 1:
The patent replaces the mechanical zero-crossing detection method with a signal processing approach using Fast Fourier Transform (FFT) to calculate phase shift. Instead of detecting zero-crossings in the time domain which is sensitive to noise, the invention transforms the signals to the frequency domain where phase can be accurately determined without being affected by time-domain noise, thus eliminating the need for aggressive low-pass filtering.
2Object-affected harmful factors
If signals are filtered in the digital domain using a robust FIR low-pass filter, then noise can be reduced, but many taps are required when the cut-off frequency is low compared to sampling frequency
Solution Approach 1:
The patent substitutes the time-domain FIR filtering approach with a frequency-domain approach using FFT-based phase calculation. By moving to the frequency domain, the system can determine phase shift directly from the spectral components without requiring complex time-domain filtering, thereby reducing computational complexity while maintaining noise rejection capabilities.
3Object-affected harmful factors
If signals are filtered in the analog domain, then filtering can be performed before digital processing, but the filters produce phase shift requiring complex filter structures with tightly tolerated components
Solution Approach 1:
The patent eliminates the need for analog filtering by performing all signal processing in the digital domain using FFT. This approach avoids the phase shift introduction problem inherent in analog filters, as the digital frequency transformation inherently preserves phase relationships when properly implemented, removing the need for complex matched filter structures.
4Measurement precision
If the resonance frequency tracking is improved using traditional methods, then the control accuracy can be enhanced, but the system complexity increases due to additional sensors and complex control loops
Solution Approach 1:
The patent implements a feedback control loop that uses FFT-based phase shift measurement to continuously track resonance frequency. The system measures the phase difference between voltage and current signals, compares it to the ideal resonant phase relationship, and adjusts the driving frequency accordingly. This feedback mechanism achieves accurate resonance tracking using standard digital signal processing capabilities already present in modern electrosurgical generators, avoiding the need for additional specialized sensors or complex hardware modifications.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively tracks changes in the mechanical resonance frequency, ensuring the ultrasonic transducer operates at optimal conditions, thereby improving the reliability and precision of electrosurgical procedures.
Implementation Method 1
Ultrasonic transducers are used to transform an alternating electrical signal into a mechanical oscillation of an electrosurgical instrument having an ultrasonic frequency
Implementation Method 2
A PLL can be used to adjust the frequency according to the measured phase shift between the voltage across the transducer and the current of the electrical equivalent of the mechanical resonance circuit
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a method for controlling an ultrasonic transducer (206) of an electrosurgical instrument (102, 202), the ultrasonic transducer (206) is driven by an alternating electrical overall current signal (im), having a signal frequency (f), driving the overall current signal (im) results in an alternating electrical instrument voltage signal (um) of the transducer (206), depending on a mechanical oscillation of the transducer (206), the instrument voltage signal (um) having a transducer phase shift with respect to a main current component of the overall current signal (im) depending on the mechanical oscillations of the transducer, the ultrasonic transducer (206) is having a fluctuating mechanical resonance frequency, an amplifier (204) is controlled to provide the electrical overall current signal (im) and adjust the signal frequency (f) towards the resonance frequency depending on the transducer phase shift, and for determining the transducer phase shift, calculating signal coefficients for the main current component and the instrument voltage signal (um), the signal coefficients being representative for a phase relationship of the main current component or the instrument voltage signal respectively with respect to a common reference signal, and calculating from the signal coefficients the transducer phase shift.