Methods for controlling temperature in ultrasonic device
A generator, ultrasonic device, and method for controlling a temperature of an ultrasonic blade are disclosed. A control circuit coupled to a memory determines an actual resonant frequency of an ultrasonic electromechanical system comprising an ultrasonic transducer coupled to an ultrasonic blade by an ultrasonic waveguide. The actual resonant frequency is correlated to an actual temperature of the ultrasonic blade. The control circuit retrieves from the memory a reference resonant frequency of the ultrasonic electromechanical system. The reference resonant frequency is correlated to a reference temperature of the ultrasonic blade. The control circuit then infers the temperature of the ultrasonic blade based on the difference between the actual resonant frequency and the reference resonant frequency. The control circuit controls the temperature of the ultrasonic blade based on the inferred temperature
1. A method for controlling an estimated temperature of an ultrasonic blade, the method comprising:
determining, by a control circuit coupled to a memory, an actual resonant frequency of an ultrasonic electromechanical system comprising an ultrasonic transducer coupled to an ultrasonic blade by an ultrasonic waveguide, wherein the actual resonant frequency is correlated to an actual temperature of the ultrasonic blade;
retrieving, from the memory by the control circuit, a reference resonant frequency of the ultrasonic electromechanical system, wherein the reference resonant frequency is correlated to a reference temperature of the ultrasonic blade;
inferring, by the control circuit, an inferred temperature of the ultrasonic blade based on a difference between the actual resonant frequency and the reference resonant frequency;
controlling, by the control circuit, the estimated temperature of the ultrasonic blade based on the inferred temperature;
generating, by the control circuit, a temperature estimator and a state space model of the inferred temperature of the ultrasonic blade as a function of the actual resonant frequency of the ultrasonic electromechanical system based on a set of non-linear state space equations;
applying, by the control circuit, a Kalman filter to improve the temperature estimator and the state space model;
applying, by the control circuit, a state estimator in a feedback loop of the Kalman filter;
controlling, by the control circuit, power applied to the ultrasonic transducer; and
regulating, by the control circuit, the estimated temperature of the ultrasonic blade,
wherein determining, by the control circuit, the actual resonant frequency of the ultrasonic electromechanical system comprises determining, by the control circuit, a phase angle φ between a voltage V g (t) and a current I g (t) signal applied to the ultrasonic transducer,
wherein the state space model is defined by:
[
F
.
n
T
.
]
=
f
(
t
,
T
(
t
)
,
F
n
(
t
)
,
E
(
t
)
)
wherein:
{dot over (F)} n represents a rate of change of a time (t) dependent natural frequency F n (t) of the ultrasonic electromechanical system;
{dot over (T)} represents a rate of change of the actual temperature of the ultrasonic blade with respect to the time (t) dependent natural frequency F n (t);
T(t) represents a time (t) dependent actual temperature of the ultrasonic blade;
E(t) represents a time (t) dependent energy;
t represents the time; and
{dot over (y)} represents an observability of variables that are measurable and observable including the time dependent natural frequency F n (t) of the ultrasonic electromechanical system, the time dependent actual temperature T(t) of the ultrasonic blade, observable as the temperature estimator, the time dependent energy E(t) applied to the ultrasonic blade, and time t, and
wherein a state variance of the state estimator of the Kalman filter is defined by:
(σ k − ) 2 =σ k-1 2 +σ P k 2 and
a gain K of the Kalman filter is defined by:
K
=
(
σ
k
_
)
2
(
σ
k
_
)
2
+
σ
m
2
.
wherein:
(σ k − ) is a variance of state k;
(σ k-1 − ) is a variance of the previous state k−1;
(σ Pk − ) is a predicted variance of state k; and
(σ m − ) is an observed system variance.
2. The method of claim 1 , wherein the control circuit and the memory are located at a surgical hub in communication with the ultrasonic electromechanical system.
3. A generator for controlling an estimated temperature of an ultrasonic blade, the generator comprising:
a control circuit coupled to a memory, the control circuit configured to:
determine an actual resonant frequency of an ultrasonic electromechanical system comprising an ultrasonic transducer coupled to an ultrasonic blade by an ultrasonic waveguide, wherein the actual resonant frequency is correlated to an actual temperature of the ultrasonic blade;
retrieve from the memory a reference resonant frequency of the ultrasonic electromechanical system, wherein the reference resonant frequency is correlated to a reference temperature of the ultrasonic blade;
infer an inferred temperature of the ultrasonic blade based on a difference between the actual resonant frequency and the reference resonant frequency;
control the estimated temperature of the ultrasonic blade based on the inferred temperature;
generate a temperature estimator and a state space model of the inferred temperature of the ultrasonic blade as a function of the actual resonant frequency of the ultrasonic electromechanical system based on a set of non-linear state space equations;
apply a Kalman filter to improve the temperature estimator and the state space model;
apply a state estimator in a feedback loop of the Kalman filter;
control power applied to the ultrasonic transducer; and
regulate the estimated temperature of the ultrasonic blade,
wherein to determine the actual resonant frequency of the ultrasonic electromechanical system, the control circuit is further configured to determine a phase angle φ between a voltage V s (t) and a current/at) signal applied to the ultrasonic transducer,
wherein the state space model is defined by:
[
F
.
n
T
.
]
=
f
(
t
,
T
(
t
)
,
F
n
(
t
)
,
E
(
t
)
)
y
.
=
h
(
t
,
T
(
t
)
,
F
n
(
t
)
,
E
(
t
)
)
.
wherein:
{dot over (F)} n represents a rate of change of a time (t) dependent natural frequency F n (t) of the ultrasonic electromechanical system;
{dot over (T)} represents a rate of change of the actual temperature of the ultrasonic blade with respect to the time (t) dependent natural frequency F n (t);
T(t) represents a time (t) dependent actual temperature of the ultrasonic blade;
E(t) represents a time (t) dependent energy;
t represents the time; and
{dot over (y)} represents an observability of variables that are measurable and observable including the time dependent natural frequency F n (t) of the ultrasonic electromechanical system, the time dependent actual temperature T(t) of the ultrasonic blade, observable as the temperature estimator, the time dependent energy E(t) applied to the ultrasonic blade, and time t, and
wherein a state variance of the state estimator of the Kalman filter is defined by:
(σ k − ) 2 =σ k-1 2 +σ P k 2 and
a gain K of the Kalman filter is defined by:
K
=
(
σ
k
_
)
2
(
σ
k
_
)
2
+
σ
m
2
.
wherein:
(σ k − ) is a variance of state k;
(σ k-1 − ) is a variance of the previous state k−1;
(σ Pk − ) is a predicted variance of state k; and
(σ m − ) is an observed system variance.
4. The generator of claim 3 , wherein the control circuit and the memory are located at a surgical hub in communication with the generator.
5. An ultrasonic device for controlling an estimated temperature of an ultrasonic blade, the ultrasonic device comprising:
a control circuit coupled to a memory, the control circuit configured to:
determine an actual resonant frequency of an ultrasonic electromechanical system comprising an ultrasonic transducer coupled to an ultrasonic blade by an ultrasonic waveguide, wherein the actual resonant frequency is correlated to an actual temperature of the ultrasonic blade;
retrieve from the memory a reference resonant frequency of the ultrasonic electromechanical system, wherein the reference resonant frequency is correlated to a reference temperature of the ultrasonic blade;
infer an inferred temperature of the ultrasonic blade based on a difference between the actual resonant frequency and the reference resonant frequency;
control the estimated temperature of the ultrasonic blade based on the inferred temperature;
generate a temperature estimator and a state space model of the inferred temperature of the ultrasonic blade as a function of the actual resonant frequency of the ultrasonic electromechanical system based on a set of non-linear state space equations;
apply a Kalman filter to improve the temperature estimator and the state space model;
apply a state estimator in a feedback loop of the Kalman filter;
control power applied to the ultrasonic transducer; and
regulate the estimated temperature of the ultrasonic blade,
wherein to determine the actual resonant frequency of the ultrasonic electromechanical system, the control circuit is further configured to determine a phase angle φ between a voltage V g (t) and a current I g (t) signal applied to the ultrasonic transducer,
wherein the state space model is defined by:
[
F
.
n
T
.
]
=
f
(
t
,
T
(
t
)
,
F
n
(
t
)
,
E
(
t
)
)
y
.
=
h
(
t
,
T
(
t
)
,
F
n
(
t
)
,
E
(
t
)
)
.
wherein:
{dot over (F)} n represents a rate of change of a time (t) dependent natural frequency F n (t) of the ultrasonic electromechanical system;
{dot over (T)} represents a rate of change of the actual temperature of the ultrasonic blade with respect to the time (t) dependent natural frequency F n (t);
T(t) represents a time (t) dependent actual temperature of the ultrasonic blade;
E(t) represents a time (t) dependent energy;
t represents the time; and
{dot over (y)} represents an observability of variables that are measurable and observable including the time dependent natural frequency F n (t) of the ultrasonic electromechanical system, the time dependent actual temperature T(t) of the ultrasonic blade, observable as the temperature estimator, the time dependent energy E(t) applied to the ultrasonic blade, and time t, and
wherein a state variance of the state estimator of the Kalman filter is defined by:
(σ k − ) 2 =σ k-1 2 +σ P k 2 and
a gain K of the Kalman filter is defined by:
K
=
(
σ
k
_
)
2
(
σ
k
_
)
2
+
σ
m
2
.
wherein:
(σ k − ) is a variance of state k;
(σ k-1 − ) is a variance of the previous state k−1;
(σ Pk − ) is a predicted variance of state k; and
(σ m − ) is an observed system variance.
6. The ultrasonic device of claim 5 , wherein the control circuit and memory are located at a surgical hub in communication with the ultrasonic device.