The first monolithic state-of-the-art controller was proposed and implemented for an electric scalpel system. A piezoelectric transducer (PT) is driven in ultrasonic resonant frequency to generate electromechanical power for thermal sealing and cold dissection operations. The band-pass filter based oscillator was developed to automatically track the PT's optimal longitudinal resonance. However, under heavy loading conditions, the PT will lock to other unwanted transverse resonant modes and deliver no usable power to the surgical tip. To prevent this abnormal operation, a phase-locked loop based frequency discriminator with intervention and release logic was developed to ensure that the PT always operates at the proper frequency of 55.5 kHz. Another crucial challenge is that the changing of loading conditions induces a motional current sensing mismatch and a pole-zero pair, consequently causing instability and poor response time. Therefore, a sliding mode control method with reduced-order sensing was proposed to handle the extreme load changes and provide a fast power build-up time of 9.2 ms, which is 8% faster than previously reported designs and 49% faster than the best commercial product. Sealing and dissection surgical operations are realized with 17.5 W maximum power.
Ultrasonic Electric Scalpels Based on a Sliding-Mode Controller With an Auxiliary PLL Frequency Discriminator.