Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEMS AND METHODS FOR IMPROVING EFFICIENCY OF
ELECTROSURGICAL GENERATORS
BACKGROUND
1. Technical Field
100011 The present disclosure relates to electrosurgery. More
particularly, the present
disclosure relates to systems and methods for improving efficiency of
electrosurgical generators.
2. Background of Related Art
100021 Electrosurgery involves the application of high-frequency electric
current to cut or
modify biological tissue during an electrosurgical procedure. Electrosurgery
is performed using
an electrosurgical generator, an active electrode, and a return electrode. The
electrosurgical
generator (also referred to as a power supply or waveform generator) generates
an alternating
current (AC), which is applied to a patient's tissue through the active
electrode and is returned to
the electrosurgical generator through the return electrode. The AC typically
has a frequency
above 100 kilohertz (kHz) to avoid muscle and/or nerve stimulation.
100031 During electrosurgery, the AC generated by the electrosurgical
generator is
conducted through tissue disposed between the active and return electrodes.
The tissue's
impedance converts the electrical energy (also referred to as electrosurgical
energy) associated
with the AC into heat, which causes the tissue temperature to rise. The
electrosurgical generator
controls the heating of the tissue by controlling the electric power (i.e.,
electrical energy per
time) provided to the tissue. Although many other variables affect the total
heating of the tissue,
increased current density usually leads to increased heating. The
electrosurgical energy is
typically used for cutting, dissecting, ablating, coagulating, and/or sealing
tissue.
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100041 The two basic types of electrosurgery employed are monopolar and
bipolar
electrosurgery. Both of these types of electrosurgery use an active electrode
and a return
electrode. In bipolar electrosurgery, the surgical instrument includes an
active electrode and a
return electrode on the same instrument or in very close proximity to one
another, usually
causing current to flow through a small amount of tissue. In monopolar
electrosurgery, the
return electrode is located elsewhere on the patient's body and is typically
not a part of the
electrosurgical instrument itself In monopolar electrosurgery, the return
electrode is part of a
device usually referred to as a return pad.
100051 Some electrosurgical generators include a controller that controls
the power
delivered to the tissue over some period of time based upon measurements of
the voltage and
current near the output of the electrosurgical generator. These generators use
a discrete Fourier
transform (DFT) or polyphase demodulation to calculate the phase difference
between
measurements of the voltage and current for calculating real power and t'or
performing
calibration and compensation.
100061 However, at low power levels, some electrosurgical generators
exhibit low
efficiencies. Thus, there is a need for improved methods of maintaining the
efficiency of
electrosurgical generators.
SUMMARY
100071 A method for controlling an output of an electrosurgical generator
includes the
steps of converting a direct current (DC) to an alternating current (AC) using
an inverter, and
sensing a current and a voltage at an output of the inverter. The method
further includes the
steps of determining a power level based on the sensed voltage and the sensed
current,
determining an efficiency of the electrosurgical generator, and inserting a
predetermined integer
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number of off cycles when the efficiency of the electrosurgical generator
reaches a threshold
power efficiency.
100081 According to a further aspect of the present disclosure, an
electrosurgical
generator includes a radio frequency (RF) amplifier coupled to an electrical
energy source and
configured to generate electrosurgical energy, the RF amplifier including: an
inverter configured
to convert a direct current (DC) to an alternating current. The
electrosurgical generator further
includes a plurality of sensors configured to sense voltage and current of the
generated
electrosurgical energy and a controller coupled to the RF amplifier and the
plurality of sensors.
The generator may further determine a power level based on the sensed voltage
and the sensed
current, determine an efficiency of the electrosurgical generator, and insert
a predetermined
integer number of off cycles when the efficiency of the electrosurgical
generator reaches a
threshold power efficiency.
100091 According to another aspect of the present disclosure a method of
improving
efficiency of an electrosurgical generator includes determining power levels
based on sensed
voltage and sensed current, determining an efficiency of the electrosurgical
generator based on
the detected power levels, and gradually dropping a predetermined integer
number of output or
off cycles when the efficiency of the electrosurgical generator reaches a
threshold power
efficiency, the predetermined integer number of output or off cycles being
randomized via a
random number generator.
BRIEF DESCRIPTION OF THE DRAWINGS
100101 Various embodiments of the present disclosure are described with
reference to the
accompanying drawings wherein:
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100111 FIG. 1 is an illustration of an electrosurgical system including a
generator, in
accordance with embodiments of the present disclosure;
100121 FIG. 2A is a block diagram of an electrosurgical system including
generator
circuitry according to a combination of a modified-Kahn technique and a Class
S generator
topology, in accordance with one embodiment of the present disclosure;
100131 FIG. 2B is a block diagram of an electrosurgical system including
generator
circuitry according to the modified-Kahn technique, in accordance with another
embodiment of
the present disclosure;
100141 FIG. 2C is a block diagram of an electrosurgical system including
generator
circuitry according to the Class S device topology, in accordance with still
another embodiment
of the present disclosure;
100151 FIG. 3 a schematic block diagram of a controller of the generator
circuitry of FIG.
2A, in accordance with an embodiment of the present disclosure;
100161 FIG. 4 is a circuit diagram illustrating switching in different
resonant components,
in accordance with an embodiment of the present disclosure; and
100171 FIGS. 5A and 5B are graphs illustrating insertion of output cycles
at
predetermined time periods, in accordance with an embodiment of the present
disclosure.
DETAILED DESCRIPTION
100181 FIG. 1 illustrates an electrosurgical system 100 in accordance with
embodiments
of the present disclosure. The electrosurgical system 100 includes an
electrosurgical generator
110 which generates electrosurgical energy to treat tissue of a patient. The
electrosurgical
generator 110 generates an appropriate level of electrosurgical energy based
on the selected
mode of operation (e.g., cutting, coagulating, ablating, or sealing) and/or
the sensed voltage and
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current waveforms of the electrosurgical energy. The electrosurgical system
100 may also
include a plurality of output connectors corresponding to a variety of
electrosurgical instruments.
100191 The electrosurgical system 100 further includes a monopolar
electrosurgical
instrument 120 having an electrode for treating tissue of the patient (e.g.,
an electrosurgical
cutting probe or ablation electrode) with a return pad 125. The monopolar
electrosurgical
instrument 120 can be connected to the electrosurgical generator 110 via one
of the plurality of
output connectors. The electrosurgical generator 110 may generate
electrosurgical energy in the
form of radio frequency (RF) energy. The electrosurgical energy is supplied to
the monopolar
electrosurgical instrument 120, which applies the electrosurgical energy to
treat the tissue. The
electrosurgical energy is returned to the electrosurgical generator 110
through the return pad 125.
The return pad 125 provides a sufficient contact area with the patient's
tissue so as to minimize
the risk of tissue damage due to the clectrosurgical energy applied to the
tissue. In addition, the
electrosurgical generator 110 and the return pad 125 may be configured to
monitor tissue-to-
patient contact to ensure that sufficient contact exists between the return
pad 125 and the patient
to minimize the risk of tissue damages.
100201 The electrosurgical system 100 also includes a bipolar
electrosurgical instrument
130, which can be connected to the electrosurgical generator 110 via one of
the plurality of
output connectors. During operation of the bipolar electrosurgical instrument,
electrosurgical
energy is supplied to one of the two jaw members, e.g., jaw member 132, of the
instrument's
forceps, is applied to treat the tissue, and is returned to the
electrosurgical generator 110 through
the other jaw member, e.g., jaw member 134.
100211 The electrosurgical generator 110 may be any suitable type of
generator and may
include a plurality of connectors to accommodate various types of
electrosurgical instruments
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(e.g., monopolar electrosurgical instrument 120 and bipolar electrosurgical
instrument 130). The
electrosurgical generator 110 may also be configured to operate in a variety
of modes, such as
ablation, cutting, coagulation, and sealing. The electrosurgical generator 110
may include a
switching mechanism (e.g., relays) to switch the supply of RF energy among the
connectors to
which various electrosurgical instruments may be connected. For
example, when an
electrosurgical instrument 120 is connected to the electrosurgical generator
110, the switching
mechanism switches the supply of RF energy to the monopolar plug. In
embodiments, the
electrosurgical generator 110 may be configured to provide RF energy to a
plurality of
instruments simultaneously.
100221 The
electrosurgical generator 110 includes a user interface having suitable user
controls (e.g., buttons, activators, switches, or touch screens) for providing
control parameters to
the electrosurgical generator 110. These controls allow the user to adjust
parameters of the
electrosurgical energy (e.g., the power level or the shape of the output
waveform) so that the
electrosurgical energy is suitable for a particular surgical procedure (e.g.,
coagulating, ablating,
tissue sealing, or cutting). The electrosurgical instruments 120 and 130 may
also include a
plurality of user controls. In addition, the electrosurgical generator 110 may
include one or more
display screens for displaying a variety of information related to operation
of the electrosurgical
generator 110 (e.g., intensity settings and treatment complete indicators).
The electrosurgical
instruments 120 and 130 may also include a plurality of input controls that
may be redundant
with certain input controls of the electrosurgical generator 110. Placing the
input controls at the
electrosurgical instruments 120 and 130 allows for easier and faster
modification of the
electrosurgical energy parameters during the surgical procedure without
requiring interaction
with the electrosurgical generator 110.
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[0023] FIG. 2A is a block diagram of generator circuitry 200 within the
electrosurgical
generator of FIG. 1. The generator circuitry 200 includes a low frequency (LF)
rectifier 220, a
direct current-to-direct current (DC/DC) converter 225, an RF amplifier 230, a
plurality of
sensors 240, analog-to-digital converters (ADCs) 250, a controller 260, a
hardware accelerator
270, a processor subsystem 280, and a user interface (UI) 290. The generator
circuitry 200 is
configured to connect to a power source 210, such as a wall power outlet or
other power outlet,
which generates alternating current (AC) having a low frequency (e.g., 25Hz,
50 Hz, or 60 Hz).
The power source 210 provides the AC power to the LF rectifier 220, which
converts the AC to
direct current (DC). Alternatively, the power source 210 and the LF rectifier
220 may be
replaced by a battery or other suitable device to provide DC power.
100241 The DC output from the LF rectifier 220 is provided to the DC/DC
converter 225
which converts the DC to a desired level. The converted DC is provided to the
RF amplifier 230,
which includes a DC-to-AC (DC/AC) inverter 232 and a resonant matching network
234. The
DC/AC inverter 232 converts the converted DC to an AC waveform having a
frequency suitable
for an electrosurgical procedure (e.g., 472 kHz, 29.5 kHz, and 19.7 kHz).
100251 The appropriate frequency for the electrosurgical energy may differ
based on
electrosurgical procedures and modes of electrosurgery. For example, nerve and
muscle
stimulations cease at about 100,000 cycles per second (100 kHz) above which
point some
electrosurgical procedures can be performed safely, i.e., the electrosurgical
energy can pass
through a patient to targeted tissue with minimal neuromuscular stimulation.
For example,
typically, ablation procedures use a frequency of 472 kHz. Other
electrosurgical procedures can
be performed at pulsed rates lower than 100 kHz, e.g., 29.5 kHz or 19.7 kHz,
with minimal risk
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of damaging nerves and muscles, e.g., Fulgurate or Spray. The DC/AC inverter
232 can output
AC signals with various frequencies suitable for electrosurgical operations.
[0026] As described above, the RF amplifier 230 includes a resonant
matching network
234. The resonant matching network 234 is coupled to the output of the DC/AC
inverter 232 to
match the impedance at the DC/AC inverter 232 to the impedance of the tissue
so that there is
maximum or optimal power transfer between the generator circuitry 200 and the
tissue.
[0027] The electrosurgical energy provided by the DC/AC inverter 232 of
the RF
amplifier 230 is controlled by the controller 260. The voltage and current
waveforms of the
electrosurgical energy output from the DC/AC inverter 232 are sensed by the
plurality of sensors
240 and provided to the controller 260, which generates control signals from a
DC/DC converter
controller 278, e.g., a pulse width modulator (PWM) or digital pulse width
modulator (DPWM)
to control the output of the DC/DC converter 225 and from a DC/AC inverter
controller 276 to
control the output of the DC/AC inverter 232. The controller 260 also receives
input signals via
the user interface (UI) 290. The Ul 290 allows a user to select a type of
clectrosurgical
procedure (e.g., monopolar or bipolar) and a mode (e.g., coagulation,
ablation, sealing, or
cutting), or input desired control parameters for the electrosurgical
procedure or the mode. The
DC/DC converter 225 of FIG. 2A may be fixed or variable depending on the power
setting or
desired surgical effects. When it is fixed, the RF amplifier behaves as a
Class S device, which is
shown in FIG. 2C. When it is variable, it behaves as a device according to the
modified-Kahn
technique, which is shown in FIG. 2B.
100281 The plurality of sensors 240 sense voltage and current at the
output of the RF
amplifier 230. The plurality of sensors 240 may include two or more pairs or
sets of voltage and
current sensors that provide redundant measurements of the voltage and
current. This
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redundancy ensures the reliability, accuracy, and stability of the voltage and
current
measurements at the output of the RF amplifier 230. In embodiments, the
plurality of sensors
240 may include fewer or more sets of voltage and current sensors depending on
the application
or the design requirements. The plurality of sensors 240 may also measure the
voltage and
current output from other components of the generator circuitry 200 such as
the DC/AC inverter
232 or the resonant matching network 234. The plurality of sensors 240 may
include any known
technology for measuring voltage and current including, for example, a
Rogowski coil.
100291 The sensed voltage and current waveforms are fed to analog-to-
digital converters
(ADCs) 250. The ADCs 250 sample the sensed voltage and current waveforms to
obtain digital
samples of the voltage and current waveforms. This is also often referred to
as an Analog Front
End (AFE). The digital samples of the voltage and current waveforms are
processed by the
controller 260 and used to generate control signals to control the DC/AC
inverter 232 of the RF
amplifier 230 and the DC/DC converter 225. The ADCs 250 may be configured to
sample the
sensed voltage and current waveforms at a sample frequency that is an integer
multiple of the RF
frequency.
100301 As shown in the embodiment of FIG. 2A, the controller 260 includes a
hardware
accelerator 270 and a processor subsystem 280. As described above, the
controller 260 is also
coupled to a Ul 290, which receives input commands from a user and displays
output and input
information related to characteristics of the electrosurgical energy (e.g.,
selected power level).
The hardware accelerator 270 processes the output from the ADCs 250 and
cooperates with the
processor subsystem 280 to generate control signals.
100311 The hardware accelerator 270 includes a dosage monitoring and
control (DMAC)
272, an inner power control loop 274, a DC/AC inverter controller 276, and a
DC/DC converter
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controller 278. All or a portion of the controller 260 may be implemented by a
field
programmable gate array (FPGA), an application specific integrated circuit
(ASIC), a digital
signal processor (DSP), and/or a microcontroller.
100321 The DMAC 272 receives samples of the sensed voltage and current
waveforms
from the ADCs 250 and calculates the average real power and the real part of
the tissue
impedance. The DMAC 272 then provides the real power and the real part of the
impedance of
the tissue to the inner power control loop 274, which generates a control
signal for the DC/AC
inverter controller 276 based on one or more of the real power and the real
part of the impedance
of the tissue. The DC/AC inverter controller 276 in turn generates a first
pulse-width modulation
(PWM) control signal to control the output of the DC/AC inverter 232.
100331 The processor subsystem 280 includes an outer power control loop
282, a state
machine 284, and a power setpoint circuit 286. The processor subsystem 280
generates a second
PWM control signal based on the output of the DMAC 272 and parameters (e.g.,
electrosurgical
mode) selected by the user via the Ul 290. Specifically, the parameters
selected by the user are
provided to the state machine 284 which determines a state or mode of the
generator circuitry
200. The outer power control loop 282 uses this state information and the
output from the
DMAC 272 to determine control data. The control data is provided to the power
setpoint circuit
286, which generates a power setpoint based on the control data. The DC/DC
converter
controller 278 uses the power setpoint to generate an appropriate PWM control
signal for
controlling the DC/DC converter 225 to converter the DC output from the LF
rectifier 220 to a
desired level. If the user does not provide operational parameters to the
state machine 284 via
the Ul 290, then the state machine 284 may maintain or enter a default state.
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100341 FIG. 3 shows a more detailed diagram or the hardware accelerator
270 of FIG. 2A.
The hardware accelerator 270 implements those functions of the generator
circuitry 200 that may
have special processing requirements such as high processing speeds. The
hardware accelerator
270 includes the DMAC 272, the inner power loop control 274, the DC/AC
inverter controller
276, and the DC/DC converter controller 278 shown in FIG. 2A.
[0035] The DMAC 272 includes four analog-to-digital converter (ADC)
controllers
312a-312d, a digital signal processor 314, RF data registers 316, and DMAC
registers 318. The
ADC controllers 312a-312d control the operation of the ADCs 250 (FIG. 2A),
which convert
sensed voltage and current waveforms into digital data. The digital data is
then provided to the
digital signal processor 314 that implements various filtering and other
digital signal processing
functions.
100361 The sensed voltage and current are the digital input to the ADCs
250, which
sample the sensed voltage and current. The ADC controllers 312a-312d provide
operational
parameters, including a predetermined sampling rate, to the ADCs 250 so that
the ADCs sample
the sensed voltage and current synchronously at a predetermined sampling rate,
i.e., a
predetermined number of samples per second, or predetermined sampling period
that is coherent
with the RF inverter frequency, i.e., an integer multiple sampling frequency
to the RF inverter
frequency. The ADC controllers 312a-312d control the operation of the ADCs
250, which
convert sensed voltage and current waveforms into digital data. The digital
data is then provided
to the digital signal processor 314 that implements various filtering and
other digital signal
processing functions.
100371 The sensed voltage and current are input to the ADCs 250, which
sample the
sensed voltage and current. The ADC controllers 312a-312d provide operational
parameters,
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including a predetermined sampling rate, to the ADCs 250 so that the ADCs
sample the sensed
voltage and current synchronously at a predetermined sampling rate, i.e., a
predetermined
number of samples per second, or predetermined sampling period. The ADC
controllers 312a-
312d may be configured to control the ADCs 250 so that the sampling period
corresponds to an
integer multiple of the RF frequency of the voltage and current waveforms.
This is often
referred to as coherent sampling.
100381 The digital data obtained by sampling the voltage and current
waveforms is
provided to the digital signal processor 314 via the ADC controllers 312a-
312d. The digital
signal processor 314 uses the digital data to calculate a complex voltage
1/c.õõ,p, a complex current
leõmp, a real power P,, and a real part of the tissue impedance 4.,,õ/.
Generally, tissue impedance
is real or resistive, but can have a small capacitive component after the
tissue is "cooked."
Further, a cable between the electrosurgical generator and the tissue also has
resistive and
reactive components. For these reasons, electrosurgical generators typically
include controls
systems that compensate for these parasities to more accurately measure the
tissue impedance.
These control systems, however, require complex computations that are
computationally
inefficient, which results in additional cost to perform the tissue impedance
calculations in a
timely manner or at update rates commensurate to the capabilities of the RF
control loop
calculations.
100391 In alternative embodiments depicted in FIGS. 2B and 2C, the hardware
accelerator is not available and many of the primary RF measurement and
control functions just
described reside instead entirely within a programmable device called an
application specific
standard product (ASSP) integrated circuit that includes at least a DSP core
processor and
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multiple digital pulse width modulators (DPWM) that are substantially similar
in function to the
hardware accelerator and its DSP and/or microcontroller core.
100401 In other embodiments, there may also be a second microprocessor
core available
within the ASSP that contains additional ADCs which may be connected to the
sensors for
performing the redundant dosage monitoring functions separately from the RF
control functions.
The second processor may also perform user interface functions such as
receiving and requesting
power settings, activation requests, and so forth for the user from the RF
controller. The ASSP
may also utilize only one RF control loop (or compensator loop), instead of
two "inner" and
"outer" compensator loops, for controlling directly any of the following:
power, voltage, current,
temperature, or impedance. This loop may use a single proportional-integral-
derivative
compensator that changes between these process variables using bumpless
transfer methods and
saturable limits.
100411 FIG. 2B shows an electrosurgical system including generator
circuitry according
to the modified-Kahn technique 201. The generator circuitry 201 includes an RF
amplifier 241
and a controller 251 for controlling the RF amplifier 241 to deliver
electrosurgical energy having
desired characteristics to tissue 247 being treated. The RF amplifier 241
receives AC or DC
from the power source 210. The RF amplifier includes an AC/DC or DC/DC
converter 242,
which converts the AC or DC provided by the power source 210 into a suitable
level of DC. As
in FIG. 2A, the RF amplifier 241 also includes a DC/AC inverter 232 which
converts the DC to
AC. The RF amplifier 241 also includes a single- or dual-mode resonant
matching network 244
and mode relays 248 for switching modes of the resonant matching network 244.
100421 The output from the RF amplifier 241 is provided to sensors 246,
which may
include voltage sensors, current sensors, and temperature sensors. The sensor
signals output
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from sensors 246 are provided to the controller 251 via an analog front end
(AFE) 252 of the
controller 251. The AFE conditions and samples the sensor signals to obtain
digital sensor data
representing the sensor signals. The controller 251 also includes a signal
processor 253, a mode
state control and bumpless transfer unit 254, a compensator or PID controller
255, a pulse width
modulator (PWM) or digital pulse width modulator (DPWM) 256, and a voltage-
controlled
oscillator or numerically-controlled oscillator 257.
100431 The signal processor 253 receives the digital sensor data and
performs the
calculations and other functions of the systems and methods according to the
present disclosure.
Among other things, the signal processor 253 calculates the real and imaginary
parts of the
sensed voltage and current, the impedance, and/or the power, and performs
functions to control
one or more of the voltage, current, power, impedance, and temperature. The
signal processor
253 also generates and provides process variables to the mode state control
and bumpless
transfer unit 254 and a compensator or PID controller 255. The mode state
control and bumpless
transfer unit 254 controls the mode relays 248 for the single or dual mode
resonant matching
network 244 according to the tissue effect algorithm, and generates and
provides coefficients and
setpoints to the compensator or PID controller 255.
100441 The compensator or PID controller 255 generates controller output
variables and
provides them to the pulse width modulator (PWM) or digital pulse width
modulator (DPWM)
256. The pulse width modulator (PWM) or digital pulse width modulator (DPWM)
256 receives
an oscillator signal from the voltage-controlled oscillator or the numerically-
controlled oscillator
257 and generates a control signal for controlling the AC/DC or DC/DC
converter 242. The
voltage-controlled oscillator or the numerically-controlled oscillator 257
also generates control
signals for controlling the DC/AC inverter 232.
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100451 Like the generator circuitry 200 of FIG. 2A, the generator
circuitry 201 includes a
user interface 290 through which a user can control and/or monitor the
functions of the generator
circuitry 201 via a controller application interface 258 of the controller
251.
100461 FIG. 2C shows an electrosurgical system including generator
circuitry according
to a Class S device topology 202. Unlike the generator circuitry 201 of FIG.
2B, the generator
circuitry 202 does not include the AC/DC or DC/DC Converter 242. An external
low-frequency
(LF) rectifier 220 or battery provides an appropriate level of DC to the DC/AC
Inverter 232 of
the RF amplifier 241. As shown in FIG. 2C, the PWM or DPWM 256 receives an
oscillator
signal from the VCO or NCO 257 and generates a control signal for controlling
the DC/AC
Inverter 232.
100471 The output of the digital signal processor 314 is provided to the
processor
subsystem 280 of FIG. 2A via RF data registers 316 (see FIG. 3). The DMAC 272
also includes
DMAC registers 318 that receive and store relevant parameters for the digital
signal processor
314 (see FIG. 3). The digital signal processor 314 further receives signals
from a PWM module
346 of the DC/AC inverter controller 276.
100481 The DMAC 272 provides a control signal to the inner power control
loop 274 via
signal line 321 and to the processor subsystem 280 via signal line 379. The
inner power control
loop 274 processes the control signal and outputs a control signal to the
DC/AC inverter
controller 276. The inner power control loop 274 includes a compensator 326,
compensator
registers 330, and VI limiter 334. The signal line 321 carries and provides a
real part of the
impedance to the compensator 326.
100491 When there is a user input, the processor subsystem 280 receives
the user input
and processes it with the outputs from the digital signal processor 314 via a
signal line 379. The
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processor subsystem 280 provides control signals via a compensator registers
330 to a VI limiter
334, which corresponds to the power setpoint circuit 286 in FIG. 2A. The VI
limiter 334 then
provides a desired power profile (e.g., a minimum and a maximum limits of the
power for a set
electrosurgical mode or operation) based on the user input and the output of
the digital signal
processor 314, the compensator registers 330 also provide other control
parameters to the
compensator 326, and then the compensator 326 combines all control parameters
from the
compensator registers 330 and the VI limiter 334, to generate output to the
DC/AC inverter
controller 276 via signal line 327.
[0050] The DC/AC inverter controller 276 receives a control parameter and
outputs
control signals that drives the DC/AC inverter 232. The DC/AC inverter
controller 276 includes
a scale unit 342, PWM registers 344, and the PWM module 346. The scale unit
342 scales the
output of the compensator registers 330 by multiplying and/or adding a number
to the output.
The scale unit 342 receives a number for multiplication and/or a number for
addition from the
PWM registers 344 via signal lines, 341a and 341 b. The PWM registers 344
store several
relevant parameters to control the DC/AC inverter 232, e.g., a period, a pulse
width, and a phase
of the AC signal to be generated by the DC/AC inverter 232 and other related
parameters. The
PWM registers 344 send signals 345a-345d to the PWM module 346. The PWM module
346
receives output from the PWM registers 344 and generates four control signals,
347a-347d, that
control four transistors of the DC/AC inverter 232 of the RF amplifier 230 in
FIG. 2A. The
PWM module 346 also synchronizes its information with the information in the
PWM registers
344 via a register sync signal 347.
100511 The PWM module 346 further provides control signals to the
compensator 326 of
the inner power control loop 274. The processor subsystem 280 provides control
signals to the
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PWM module 346. In this way, the DC/AC inverter controller 276 can control the
DC/AC
inverter 232 of the RF amplifier 230 with integrated internal input (i.e.,
processed results from
the plurality of sensors by the DMAC 272) and external input (i.e., processed
results from the
user input by the processor subsystem 280).
190521 The processor subsystem 280 also sends the control signals to the
DC/DC
converter controller 278 via signal line 373. The DC/DC converter controller
278 processes the
control signals and generates another control signals so that the DC/DC
converter 225 converts
direct current to a desired level suitable for being converted by the RF
amplifier 230. The
DC/DC converter controller 278 includes PWM registers 352 and a PWM module
354. The
PWM registers 352 receive outputs from the processor subsystem 280 via signal
line 373 and
stores relevant parameters as the PWM registers 344 does. The PWM registers
352 send signals
353a-353d to the PWM module 354. The PWM module 354 also sends a register sync
signal to
the PWM registers 352 and generates four control signals, 355a-355d, that
control four
transistors of the DC/DC converter 225 in FIG. 2A.
100531 FIG. 4 is a circuit diagram 400 illustrating switching in different
resonant
components, in accordance with an embodiment of the present disclosure. The
circuit diagram
400 illustrates mode relays 248 and matching network 244. The mode relays 248
allow a user to
switch between different operating modes. For example, the top mode relay 248
allows a user to
switch between a cut mode and a spray mode, whereas the bottom mode relay 248
allows a user
to switch between a ligature mode and a blend mode. One skilled in the art may
contemplate a
plurality of relays for switching between a plurality of operating modes.
Additionally, the
capacitors 410 and the inductors 420 are appropriately sized for the selected
mode. The
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CA 02860197 2014-08-22
matching network 244 includes two transformers 430 to vary the relative
voltage of the circuit
400 and provide for patient isolation.
100541 The preceding description provides a detailed account of the
components and
devices for controlling the output of an electrosurgical generator 110.
Typically, the manner in
which average power output from a DC/AC inverter (and then applied to a
patient) is reduced is
by reducing the pulse width of the PWM signal output by the DC/AC inverter
controller 276 (Fig.
2A). However, power control in this manner can result in a loss of efficiency
when operating a
low power setting.
100551 FIG. 5A depicts an output signal of the DC/AC inverter controller
276 (Fig. 2A)
and particularly the PWM module 346 (FIG. 3), which control the DC/AC inverter
232. In FIG.
5A, the initial signal is a continuous wave (CW) controlling the DC/AC
inverter 232. The pulses
(i.e., the high and low signals) of the CW have a short pulse width TPwHigh.
By shortening the
pulse width, the average power output by the DC/AC inverter 232, and
ultimately applied to the
patient, is reduced. As noted above, however, mere reduction in the pulse
width when using a
CW can result in efficiency losses as the average power output is reduced.
100561 According to one embodiment of the present disclosure, the
efficiency of the
DC/AC inverter 232 may be increased by lengthening the pulse width to TPW1 ow,
and
transitioning from a CW to a pulsed wave (PW) with a 50% duty cycle. In other
words, pulses
are only sent to the DC/AC inverter 232 during 50% of a period T. In the
example of FIG. 5A,
during the period T, four cycles of pulsed signals are produced during a
period Tor, followed by
no signal being produced for a period Toff, which is also four cycles, thus
Too and Toil- are equal
(i.e., represent the same period of time). Further, in this example, by
lengthening the pulse width
TP\vi õ, to approximately twice TPwiligh, the average power output by the
DC/AC inverter 232
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may be maintained. However, because of the decrease in the number of
switchings that occur at
the DC/AC inverter 232, an increase of the time between such switchings (i.e.,
TPwLow >
TPwHigh), and a period Toff where no switchings occur, an increase in
efficiency is achieved as
compared to simply reducing the pulse width of a CW.
[0057] In an alternative or additional embodiment, the efficiency at low
power levels
may be improved by dropping or deactivating at least some predetermined
integer number of
output cycles. As shown in FIG. 5B, the duty cycle of the PW which is supplied
to the DC/AC
inverter 232 remains at 50%. However, rather than a PW where a period T. is
followed by a
period Toff, where periods T. and Toff are equal, the periods of Toff may be
randomly dispersed
in the period T, as represented by the periods of no signal 510. The aggregate
time for the
periods of no signal 510 are equivalent to Toff (shown in FIG. 5A), and result
in the same output
from the DC/AC inverter, when the amplitude of the current remains constant.
[0058] The result of the signaling schemes depicted in FIGS. 5A and 5B is
that two time
parameters are employed in achieving a desired average power. The first is the
overall duty
cycle (shown as 50%) whereby no signal is supplied during Toff or half of the
period T. The
other is the pulse width (e.g., TPwLow) of the signal supplied during T.,
resulting in greater
control and greater efficiency when low powers are desired for use by a
clinician. As an
example, lower power may be 10% of rated power of the electrosurgical
generator 110.
[0059] It is noted that the efficiency may be determined by the
controller 260. However,
in certain circumstances, the efficiency may not be determined by the
controller 260, but with
other external efficiency computing components/elements. Reference is made to
U.S.
Provisional Patent No. 61/838,753 (attorney docket number H-EM-00182PR0 (203-
9554PR0))
entitled "DEAD-TIME OPTIMIZATION OF RESONANT INVERTERS"
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Date Recue/Date Received 2020-12-17
for alternative online and/or offline methods of determining efficiency. For
example, the
efficiency of the system may be characterized offline and the off cycles may
be inserted when a
predetermined threshold is reached for a control parameter, such as, duty
cycle or phase, or when
a sensed power drops below a certain threshold.
[0060] Moreover, the dropped cycles, within any given time period, may be
randomized
by using a pseudo-random sequence determined by a random number generator. The
random
number generator may be, for example, a Galois sequence that spreads out the
spectrum in order
to mitigate any undesirable frequencies. As a result, a useful range of
operation of the
electrosurgical generator 110 may be extended, while maintaining reasonable
energy conversion
efficiency.
[0061] It is to be understood that the disclosed embodiments are merely
exemplary of the
disclosure, which can be embodied in various forms. Therefore, specific
structural and
functional details disclosed herein are not to be interpreted as limiting, but
merely as a
representative basis for teaching one skilled in the art to variously employ
the present disclosure
in virtually any appropriately detailed structure. Further, the terms and
phrases used herein are
not intended to be limiting; but rather, to provide an understandable
description of the disclosure.
[0062] It is to be understood that the terminology used herein is for the
purpose of
describing particular embodiments only and is not intended to be limiting. In
this document, the
terms "a" or "an", as used herein, are defined as one or more than one. The
term "plurality," as
used herein, is defined as two or more than two. The term "another," as used
herein, is defined
as at least a second or more. The terms "including" and/or "having," as used
herein, are defined
as comprising (i.e., open language). The term "coupled," as used herein, is
defined as connected,
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Date Recue/Date Received 2020-12-17
CA 02860197 2014-08-22
although not necessarily directly, and not necessarily mechanically.
Relational terms such as
first and second, top and bottom, and the like may be used solely to
distinguish one entity or
action from another entity or action without necessarily requiring or implying
any actual such
relationship or order between such entities or actions. The terms "comprises,"
"comprising," or
any other variation thereof are intended to cover a non-exclusive inclusion,
such that a process,
method, article, or apparatus that comprises a list of elements does not
include only those
elements but may include other elements not expressly listed or inherent to
such process, method,
article, or apparatus. An element proceeded by "comprises ... a" does not,
without more
constraints, preclude the existence of additional identical elements in the
process, method, article,
or apparatus that comprises the element.
190631 As used herein, the term "about" or "approximately" applies to all
numeric values,
whether or not explicitly indicated. These terms generally refer to a range of
numbers that one of
skill in the art would consider equivalent to the recited values (i.e., having
the same function or
result). In many instances these terms may include numbers that are rounded to
the nearest
significant figure. In this document, the term "longitudinal" should be
understood to mean in a
direction corresponding to an elongated direction of the object being
described. Finally, as used
herein, the terms "distal" and "proximal" are considered from the vantage of
the user or surgeon,
thus the distal end of a surgical instrument is that portion furthest away
from the surgeon when in
use, and the proximal end is that portion generally closest to the user.
[00641 It will be appreciated that embodiments of the disclosure described
herein may be
comprised of one or more conventional processors and unique stored program
instructions that
control the one or more processors to implement, in conjunction with certain
non-processor
circuits and other elements, some, most, or all of the functions of ultrasonic
surgical instruments
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described herein. The non-processor circuits may include, but are not limited
to, signal drivers,
clock circuits, power source circuits, and user input and output elements.
Alternatively, some or
all functions could be implemented by a state machine that has no stored
program instructions, in
one or more application specific integrated circuits (ASICs), in which each
function or some
combinations of certain of the functions are implemented as custom logic, or
in a field-
programmable gate array (FPGA) enabling the use of updateable custom logic
either by the
manufacturer or the user. Of course, a combination of the three approaches
could also be used.
Thus, methods and means for these functions have been described herein.
[0065]
From the foregoing, and with reference to the various figure drawings, those
skilled in the art will appreciate that certain modifications may also be made
to the present
disclosure without departing from the scope of the same. While several
embodiments of the
disclosure have been shown in the drawings and/or described herein, it is not
intended that the
disclosure be limited thereto, as it is intended that the disclosure be as
broad in scope as the art
will allow and that the specification be read likewise. Therefore, the above
description should
not be construed as limiting, but merely as exemplifications of particular
embodiments.
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Date Recue/Date Received 2020-12-17
