Temperature control of ultrasonic end effector and control system therefor
A generator, ultrasonic device, and method of determining 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.
1. A method of determining an inferred 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 the 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; and
calculating, by the control circuit, the inferred temperature of the ultrasonic blade with a set of non-linear state space equations based on-a difference between-the actual resonant frequency and the reference resonant frequency.
2. The method of claim 1 , 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.
3. The method of claim 2 , further comprising generating, by the control circuit, a temperature estimator and 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 the set of non-linear state space equations.
4. The method of claim 3 , 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 the state space model represents the rate of change of the actual resonant frequency of the ultrasonic electromechanical system {dot over (F)} n and the rate of change of the temperature {dot over (T)} of the ultrasonic blade with respect to the actual resonant frequency F n (t), temperature T(t), energy E(t), and time t, and wherein {dot over (y)} represents the observability of variables that are measurable.
5. The method of claim 4 , further comprising applying, by the control circuit, a Kalman filter to improve the temperature estimator and the state space model.
6. The method of claim 5 , further comprising:
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 inferred temperature of the ultrasonic blade.
7. The method of claim 6 , 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 defined as the state variance, P is probability, and σ m is the observation variance.
8. 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.
9. A generator for determining an inferred 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 the 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; and
calculate the inferred temperature of the ultrasonic blade with a set of non-linear state space equations based on a difference between the actual resonant frequency and the reference resonant frequency.
10. The generator of claim 9 , 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.
11. The generator of claim 10 , wherein the control circuit is further configured to generate a temperature estimator and 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 the set of non-linear state space equations.
12. The generator of claim 11 , 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 the state space model represents the rate of change of the actual resonant frequency of the ultrasonic electromechanical system {dot over (F)} n and the rate of change of the temperature {dot over (T)} of the ultrasonic blade with respect to the actual resonant frequency F n (t), temperature T(t), energy E(t), and time t, and wherein {dot over (y)} represents the observability of variables that are measurable.
13. The generator of claim 12 , wherein the control circuit is further configured to apply a Kalman filter to improve the temperature estimator and the state space model.
14. The generator of claim 13 , wherein the control circuit is further configured to:
apply a state estimator in a feedback loop of the Kalman filter;
control power applied to the ultrasonic transducer; and
regulate the inferred temperature of the ultrasonic blade.
15. The generator of claim 14 , 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 defined as the state variance, P is probability, and σ m is the observation variance.
16. An ultrasonic device for determining an inferred 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 the 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; and
calculate the inferred temperature of the ultrasonic blade with a set of non-linear state space equations based on a difference between the actual resonant frequency and the reference resonant frequency.
17. The ultrasonic device of claim 16 , 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.
18. The ultrasonic device of claim 17 , wherein the control circuit is further configured to generate a temperature estimator and 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 the set of non-linear state space equations.
19. The ultrasonic device of claim 18 , 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 the state space model represents the rate of change of the actual resonant frequency of the ultrasonic electromechanical system {dot over (F)} n and the rate of change of the temperature {dot over (T)} of the ultrasonic blade with respect to the actual resonant frequency F n (t), temperature T(t), energy E(t), and time t, and wherein {dot over (y)} represents the observability of variables that are measurable.
20. The ultrasonic device of claim 19 , wherein the control circuit is further configured to apply a Kalman filter to improve the temperature estimator and the state space model.
21. The ultrasonic device of claim 20 , wherein the control circuit is further configured to:
apply a state estimator in a feedback loop of the Kalman filter;
control power applied to the ultrasonic transducer; and
regulate the inferred temperature of the ultrasonic blade.
22. The ultrasonic device of claim 21 , 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 defined as the state variance, P is probability, and σ m is the observation variance.