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 .- 24 . (canceled)
25 . A method of controlling an ultrasonic blade couple to an ultrasonic transducer, the method comprising:
supplying, by a generator, a power at a frequency to the ultrasonic transducer;
iteratively determining, by a controller, an inferred temperature of the ultrasonic blade by a state space model, wherein the state space model is based on the power and the frequency supplied by the generator;
applying, by the controller, a Kalman filter to update a state space estimator of the state space model,
wherein the Kalman filter comprises a state variance of the state space estimator,
wherein the state variance is defined by
(
σ
k
-
)
2
=
σ
k
-
1
2
+
σ
P
k
2
wherein
(σ k − ) is a variance of state k,
(σ k-1 ) is a variance of the previous state k−1, and
(σ Pk ) is a predicted variance of state k; and
adjusting, by the controller, the power supplied by the generator to the ultrasonic transducer based on the inferred temperature of the ultrasonic blade.
26 . The method of claim 25 , further comprising generating, by the controller, a temperature estimator of the ultrasonic blade as a function of a resonant frequency of the ultrasonic blade based on a set of non-linear state space equations.
27 . The method of claim 26 , further comprising determining, by the controller, an actual resonant frequency of the ultrasonic blade wherein the actual resonant frequency is correlated to an actual temperature of the ultrasonic blade.
28 . The method of claim 27 , wherein the Kalman filter 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 blade;
{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 the observability of variables that are measurable and observable including the time dependent natural frequency F n (t) of the ultrasonic blade, the time dependent actual temperature T(t) of the ultrasonic blade, observable as the estimated temperature, the time dependent energy E(t) applied to the ultrasonic blade, and time t,.
28 . The method of claim 25 , further comprising determining, by the controller, a phase angle φ between a voltage V g (t) and a current I g (t) signal applied to the ultrasonic transducer.
29 . The method of claim 25 , further comprising:
applying, by the controller, a state estimator in a feedback loop of the Kalman filter;
controlling, by the controller, the power applied to the ultrasonic transducer; and
regulating, by the controller, a temperature of the ultrasonic blade.
30 . The method of claim 25 , further comprising determining, by the controller, a gain K of the Kalman filter, wherein the gain K is defined by
K
=
(
σ
k
-
)
2
(
σ
k
-
)
2
+
σ
m
2
.
wherein (σ m 2 ) is an observed system variance.
31 . The method of claim 25 , further comprising retrieving, from a memory by the controller, a reference resonant frequency of the ultrasonic blade, wherein the reference resonant frequency is correlated to a reference temperature of the ultrasonic blade.
32 . The method of claim 31 , further comprising retrieving, from the memory by the controller, a reference resonant frequency of the ultrasonic blade, wherein the reference resonant frequency is correlated to a reference temperature of the ultrasonic blade.