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* cited by examiner

1

AUTOMATIC CONTROL SYSTEM FOR AN
ELECTROSURGICAL GENERATOR

CROSS REFERENCE TO RELATED

APPLICATIONS: 5

This application claims the benefit of U.S. Provisional Application No. 60/515,816, filed Oct. 30, 2003.

BACKGROUND OF THE INVENTION 10

1. Technical Field

The present disclosure relates to electrosurgery. More particularly, the present disclosure relates to an automatic control system for an electrosurgical generator. 15

2. Background of Related Art

Surgeons have tried to deal with energy application by adjusting the basic power level of the electrosurgical generator and using a hand or foot switch to control the power applied over time. Unfortunately, that technique often leads 20 to unintended power delivery or undesired duration of power delivery to the surgical site. Surgeons also experience difficulty in repeatably and/or consistently desiccating tissue to the desired levels due to the user's reaction time and/or machine response time when manual or foot activated 25 switches are used for manual control. In addition, during endoscopic procedures, visual and tactile feedback is diminished.

A circuit for automatically controlling the output of an electrosurgical generator is disclosed in U.S. Pat. No. 6,210, 30 403 to Klicek, currently owned, and assigned to Sherwood Services AG, the contents of which are hereby incorporated by reference in its entirety. U.S. Pat. No. 6,210,403 relates to an electrosurgical generator control, which is responsive to the tissue impedance between the active and return 35 electrodes during desiccation.

A method for tone detection using the Goertzel algorithm is disclosed in an article entitled The Goertzel Algorithm by Kevin Banks {The Goertzel Algorithm by Kevin Banks, <http://www.embedded.com/showArticle.jhtml7arti- 40 cleID=9900772>, last visited on Jul. 24, 2003). The Banks' article relates to using a modified Goertzel algorithm for determining whether a tone of a specific frequency is present. The Goertzel algorithm calculates both the magnitude and the phase of signal at a specific frequency and is 45 functionally equivalent to performing a Discrete Fourier Transform (DFT) at a single frequency, but is much less computationally demanding. The DFT is a method for calculating the magnitude and phase of a band of frequencies of interest. An N-point DFT is computationally demand- 50 ing, but will calculate the real and imaginary frequency terms for all the frequencies up to half the sampling rate of the signal.

According to Banks, using a modified Goertzel algorithm is preferable in applications requiring tone detection such as 55 DTMF, call progress decoding, and frequency response measurements. However, the modified Goertzel algorithm proposed by Banks does not provide the real and imaginary frequency components of the sampled waveform. As a result, the modified Goertzel algorithm is unsuited for deter- 60 mining the phase of the waveform.

It is an object of the present disclosure to provide an automatic control system that uses fewer computational steps.

Another object of the present disclosure is to provide an 65 automatic control system that measures the power delivered to a patient.

2

Yet a further object of the present disclosure is to provide an automatic control system that is adaptable to both monopolar and bipolar electrosurgical generator configurations.

It is a further object of the present disclosure to provide an automatic control system that adjusts the power delivered to a patient by an electrosurgical generator.

SUMMARY

An automatic control system for an electrosurgical generator is hereinafter disclosed. The automatic control system includes voltage and current sensing circuits, a processing circuit, an output determining circuit, and a control circuit. The voltage and current sensing circuits produce voltage and current signals that are representative of the voltage and current present in the output of the electrosurgical generator. These signals are coupled to the processing circuit that uses a Goertzel algorithm to determine the phase difference between the voltage waveform and the current waveform according to circuitry within the processing circuit.

The processing circuit produces a phase difference signal that is communicated to the output determining circuit for determining the output of the electrosurgical generator. The output determining circuit produces an output signal that is compared to a reference signal in the control circuit. The control circuit determines the difference between the output signal and the reference signal and generates a feedback signal that is representative of the difference. The feedback signal is communicated to a drive control circuit for controlling the output of a drive circuit.

Preferably, the Goertzel algorithm determines phase angle between the voltage waveform and the current waveform. Advantageously, the phase angle is used to compensate for energy delivery at the operating site. It is also contemplated that the phase angle can be utilized to provide feedback to the generator about tissue relating to at least one of: tissue change over time, tissue impedance, tissue type, tissue cycle completion.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the presently disclosed are described herein with reference to the drawing, wherein:

FIG. 1 is block diagram of an automatic control system for an electrosurgical generator in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the presently disclosed automatic control system will now be described in detail with reference to the drawing where, in FIG. 1, an exemplary embodiment of the presently disclosed automatic control system 10 is illustrated. Automatic control system 10 is ideally disposed within an electrosurgical generator 11. Electrosurgical generator 11 includes a user control 16 preferably on its front panel accessible to the doctor for setting the output level desired for a particular electrosurgical procedure. User control 16 may be a knob, a slider, or other structures and/or devices as is known in the art for use by the doctor to set a reference signal 26 indicative of the desired output.

A voltage sensing circuit 17 has an isolation transformer, which acts as an inductive pickup. Its primary side is electrically connected between leads 14 and 15 for inducing a voltage signal 18 on the secondary windings thereby responding to the high frequency electrosurgical energy supplied by electrosurgical generator 11 flowing through leads 14 and 15. A current sensing circuit 19 responds to high frequency electrosurgical energy supplied by electrosurgical generator 11 and flowing through return lead 15. Current sensing circuit 19 provides a current signal 20 as an instantaneous output representative of the current passing therethrough. Preferably, voltage signal 18 and current signal 20 are AC waveforms that are representative of the output of leads 14 and 15.

Operatively connected to leads 14 and 15 are electrodes

12 and 13. Electrodes 12 and 13 are used to provide the output of electrosurgical generator 11 to a patient. In a bipolar configuration, electrodes 12 and 13 are both present in an electrosurgical instrument (not shown), which is used at a surgical site of the patient with electrode 13 providing the return path for the output of electrosurgical generator 11.

In a monopolar configuration, the electrosurgical instrument (not shown) includes one electrode 12 while electrode

13 is connected to a surface near the patient and provides the return path. The active ends of electrodes 12 and 13 are electrically connected to electrosurgical generator 11 by one or more conductive cables. Although monopolar and bipolar configurations are used in electrosurgical generators, they are electrically equivalent and equally suited for use with automatic control system 10 of the present disclosure.

Voltage sensing circuit 17 and current sensing circuit 19 are operatively coupled to a processing circuit 21. In a preferred embodiment, processing circuit 21 includes one or more digital signal processors (DSP) and associated circuitry. The DSPs may be upgradeable using flash ROM as is known in the art. Upgrades for the DSPs may be stored on computer readable media such as magnetic disks, optical disks, magnetic tape, or other media as is known in the art. Processing circuit 21 simultaneously receives voltage signal 18 and current signal 20.

In a preferred embodiment, processing circuit uses the Goertzel algorithm for processing voltage and current signals 18, 20. The Goertzel algorithm is advantageously implemented as a second order recursive infinite impulse response filter, as shown below.

The Goertzel algorithm is defined by the equation:

The Goertzel algorithm is implemented digitally as:

Since the output frequency of electrosurgical generator 11 is known, and preferably, about 470 KHz, the digitally implemented Goertzel algorithm calculates the real and imaginary frequency components of the known waveform using the following formulae:

Real=(vi/K-l]-(vi/K-2]*cos (2xk/N))
Imaginary=(vfr/K-2]*sin (2xk/N))
Magnitude=square_root (Real2+Imaginary2)
Phase=ATAN (Imaginary/Real)

The DSPs of processing circuit 21 calculates the Voltage_Phase for voltage signal 18 and the Current_Phase for current signal 20 according to the above-mentioned formulae. Additionally, the phase shift, preferably in radians, between voltage signal 18 and current signal 20 can then be calculated by applying the algorithm on voltage signal 18 and current signal 20 concurrently and subtracting the difference in the phases as follows:

Phase_DifTerence=Current_Phase-Voltage_Phase.

This phase calculation is implemented to calculate the phase differential between voltage signal 18 and current signal 20. In the preferred embodiment, the DSPs of processing circuit 21 include the Goertzel algorithm along with associated processing software to determine the phase difference between voltage signal 18 and current signal 20. Additionally, processing circuit 21 determines a magnitude value of both voltage and current signals 18, 20 and communicates these values along with the Phase_Difference to an output determining circuit 24 as phase difference signal 22.

In one embodiment, output determining circuit 24 includes a microprocessor with associated circuitry for calculating the dosage (current, power or voltage) output of electrosurgical generator 11 using the calculated Phase_Difference and values of the voltage and current outputs of electrosurgical generator 11. In an AC circuit, power is determined by the formula P=EI cos (q), where P is the power measured in watts, E is a voltage value, I is a current value, and q is the Phase_Difference between the voltage and current waveforms.

By advantageously using the Goertzel algorithm for a single known value of frequency, automatic control system 10 of the present disclosure calculates the output for electrosurgical generator 11 using fewer computational steps than a DFT. More particularly, due to the frequency of the output and the selected sampling rate for the voltage and current components of the output, there is insufficient bandwidth to use a DFT to determine the Phase_Difference. However, processing circuit 21, according to the present disclosure, determines the Phase_Difference using the Goertzel algorithm, thereby using fewer computational steps and within the existing bandwidth. As used herein, bandwidth refers to the time between the voltage and/or current samples acquired by voltage and current sensing circuits 17, 19.

Preferably, automatic control system 10 additionally calculates the output of electrosurgical generator 11 and per