Method for detecting three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing
A method for detecting a three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing, including: pre-preparing a three-dimensional force sensor, including a clamp head, an elastomer, and a transmission component; three groups of etched stepped reduced-diameter fiber gratings are provided on the elastomer; constructing, when the clamp head of the three-dimensional force sensor clamps the tissues, a mechanical model of the elastomer, establishing a relationship between central wavelength drift amounts of the etched stepped reduced-diameter fiber gratings and a temperature as well as the three-dimensional force, and deriving a force and temperature sensitivity matrix; decoupling central wavelength values of the three groups of etched stepped reduced-diameter fiber gratings to measure the three-dimensional force and the temperature; using a long short-term memory neural network to train network parameters; and outputting types of the tissues clamped by the clamp in a classified manner through a random forest algorithm.
1 . A method for detecting a three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing, comprising the following steps:
S 1 : pre-preparing a three-dimensional force sensor, wherein the three-dimensional force sensor comprises a clamp head ( 1 ), an elastomer ( 2 ), and a transmission component, one end of the elastomer ( 2 ) in an axial direction is connected with the clamp head ( 1 ), and the clamp head ( 1 ) is configured to clamp tissues; another end of the elastomer ( 2 ) in the axial direction is provided with the transmission component, and the transmission component passes through the elastomer ( 2 ) to be in a transmission connection with the clamp head ( 1 ); and three groups of etched stepped reduced-diameter fiber gratings ( 7 ) are provided on the elastomer ( 2 ) in a centrosymmetric distribution;
S 2 : constructing, when the clamp head ( 1 ) of the three-dimensional force sensor clamps the tissues, a mechanical model of the elastomer ( 2 ), obtaining a strain of the elastomer ( 2 ) under action of the three-dimensional force, establishing, in combination with temperature sensitivity coefficients of the three groups of etched stepped reduced-diameter fiber gratings ( 7 ), a relationship between central wavelength drift amounts of the etched stepped reduced-diameter fiber gratings ( 7 ) and a temperature as well as the three-dimensional force, and deriving a force and temperature sensitivity matrix;
S 3 : decoupling, by solving a generalized inverse matrix of the force and temperature sensitivity matrix as a calibration matrix, central wavelength values of the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) to measure the three-dimensional force and the temperature;
S 4 : filtering three-dimensional force time series data, constructing a training sample, and using a long short-term memory (LSTM) neural network to train network parameters; and predicting three-dimensional force data at a current moment and recovering subsequent interaction force measurement data after training is completed, according to a sample corresponding to current input three-dimensional force data and in combination with historical fault-free three-dimensional force data and fault-free three-dimensional force data prior to the current moment, and realizing a fault-tolerant output of three-dimensional force decoupling under a fault of the etched stepped reduced-diameter fiber gratings ( 7 ); and
S 5 : outputting types of the tissues clamped by the clamp in a classified manner through a random forest algorithm in combination with central wavelength drift amount information of the three groups of etched stepped reduced-diameter fiber gratings ( 7 ).
2 . The method for detecting the three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing according to claim 1 , wherein the elastomer ( 2 ) comprises a hollow double-layer cylinder ( 12 ), two diaphragms ( 11 ), and a plurality of curved connection portions; an inner cylinder is coaxially provided at an inner center of an outer cylinder of the double-layer cylinder ( 12 ), and two axially extending end portions of the inner cylinder are fixedly connected with two axially extending end portions of the outer cylinder respectively; an axially penetrating first through hole ( 100 ) is provided at centers of the end portions of the outer cylinder, and the first through hole ( 100 ) communicates with an interior of the inner cylinder: a plurality of penetrating second through holes ( 200 ) are formed on an end face located between an inner surface of the outer cylinder and an outer surface of the inner cylinder, and the second through holes ( 200 ) extend in an axial direction of the outer cylinder and are provided in a penetrating manner; the plurality of second through holes ( 200 ) are provided in centrosymmetry with respect to the first through hole ( 100 );
the two diaphragms ( 11 ) are provided in a spaced manner on outer sides of the axially extending ends of the outer cylinder and spaced apart from the outer cylinder, a center of each of the two diaphragms ( 11 ) is provided with a penetrating third through hole ( 300 ), edges of the two diaphragms ( 11 ) are further provided with a plurality of optical fiber fixing holes ( 8 ), and the optical fiber fixing holes ( 8 ) are provided in a penetrating manner in the axial direction of the outer cylinder, and further extend outward in a radial direction of the diaphragms ( 11 ); the third through holes ( 300 ) and the first through hole ( 100 ) communicate with each other; the plurality of second through holes ( 200 ) and the plurality of optical fiber fixing holes ( 8 ) are provided in a one-to-one correspondence and mutual communication; and diameters of the two diaphragms ( 11 ) are approximately equal a diameter of the outer cylinder;
the plurality of curved connection portions are provided between the two diaphragms ( 11 ) and end faces of the outer cylinder, the curved connection portions are fixedly connected with the two diaphragms ( 11 ) and the outer cylinder respectively, one ends of the curved connection portions close to the outer cylinder are tangent to contours of the second through holes ( 200 ), and one ends of the curved connection portions away from the outer cylinder are flush with edges of the optical fiber fixing holes ( 8 ); inner surfaces of the plurality of curved connection portions are located on the same virtual cylinder, the virtual cylinder and the inner cylinder are coaxially provided, and a diameter of the virtual cylinder is larger than that of the first through hole ( 100 ), and the diameter of the virtual cylinder is smaller than an inner diameter of the outer cylinder;
the transmission component passes through the first through hole ( 100 ) and the third through holes ( 300 ) sequentially and is in a transmission connection with the clamp head ( 1 ); and the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) pass through the optical fiber fixing holes ( 8 ) and the second through holes ( 200 ), and parts of the step reducing fiber gratings between the two diaphragms ( 11 ) are in a suspended-tensioned state, and a length of suspended and tensioned sections of the step reducing fiber gratings is the same as an axial length of the outer cylinder.
3 . The method for detecting the three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing according to claim 2 , wherein the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) each comprise a metallized optical fiber, the metallized optical fiber is provided with a grating region, and the grating region comprises a normal section and a etched stepped reduced-diameter section provided sequentially; and metal nickel-plated layers are provided in a spaced manner at two ends of the grating region in an axially extending direction, and the metal nickel-plated layer is fixedly connected with an inner surface of the optical fiber fixing hole ( 8 ).
4 . The method for detecting the three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing according to claim 3 , wherein a method for preparing the elastomer ( 2 ) is: processing the outer cylinder, the inner cylinder, the two diaphragms ( 11 ), and the plurality of curved connection portions through a method of additive manufacturing of printing a titanium alloy powder, reserving a half of each of the second through holes ( 200 ) and the optical fiber fixing holes ( 8 ), afterwards, placing the etched stepped reduced-diameter fiber grating ( 7 ) in the correspondingly provided half of the second through hole ( 200 ) and optical fiber fixing hole ( 8 ), next preparing the complete second through hole ( 200 ) and optical fiber fixing hole ( 8 ) by laser scanning printing of the titanium alloy powder to fix the etched stepped reduced-diameter fiber grating ( 7 ), and then providing the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) and the transmission component on the elastomer ( 2 ) sequentially in a penetrating manner.
5 . The method for detecting the three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing according to claim 3 , wherein step S 2 is specified as:
the three-dimensional force sensor is affected by an axial force Fz, a transverse force F X , a longitudinal force F y , and the temperature;
when the three-dimensional force sensor is only subjected to action of the axial force Fz, strains of the suspended and tensioned sections of the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) are: ε Fz1 =ε Fz2 =ε Fz3 =ε Fz ; then when the elastomer ( 2 ) is only subjected to the action of the axial force Fz, wavelength drifts corresponding to the normal sections and the etched stepped reduced-diameter sections of the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) are:
{
Δ
λ
1
-
n
=
C
1
+
C
λ
1
-
n
(
1
-
P
e
)
ε
Fz
=
K
z
1
-
n
Δ
λ
1
-
e
=
1
1
+
C
λ
1
-
e
(
1
-
P
e
)
ε
Fz
=
K
z
1
-
e
Δ
λ
2
-
n
=
C
1
+
C
λ
2
-
n
(
1
-
P
e
)
ε
Fz
=
K
z
2
-
n
Δ
λ
2
-
e
=
1
1
+
C
λ
2
-
e
(
1
-
P
e
)
ε
Fz
=
K
z
2
-
e
Δ
λ
3
-
n
=
C
1
+
C
λ
3
-
n
(
1
-
P
e
)
ε
Fz
=
K
z
3
-
n
Δ
λ
3
-
e
=
1
1
+
C
λ
3
-
e
(
1
-
P
e
)
ε
Fz
=
K
z
3
-
e
,
where Δλ i-n and Δλ i-e are wavelength drift amounts of central wavelengths generated by the normal section and the etched stepped reduced-diameter section of the suspended-tensioned etched stepped reduced-diameter fiber grating ( 7 ) respectively, λ i-n and λ i-e are initial central wavelengths of the normal section and the etched stepped reduced-diameter section of the suspended-tensioned etched stepped reduced-diameter fiber grating ( 7 ) respectively, and i=1,2,3; C′ is a strain sensitivity ratio of the normal section and the etched stepped reduced-diameter section of the etched stepped reduced-diameter fiber grating ( 7 ); K zi-n and K zi-e are force sensitivities of the normal section and the etched stepped reduced-diameter section of the etched stepped reduced-diameter fiber grating ( 7 ) when the elastomer ( 2 ) is only subjected to the action of the axial force Fz; and P e is an effective elastic-optic constant of a fiber core of the optical fiber;
when the three-dimensional force sensor is only subjected to action of the transverse force F X ; the elastomer ( 2 ) undergoes a transverse deformation, the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) are named a first etched stepped reduced-diameter fiber grating, a second etched stepped reduced-diameter fiber grating, and a third etched stepped reduced-diameter fiber grating respectively; the first etched stepped reduced-diameter fiber grating undergoes a deformation in a direction opposite to the second etched stepped reduced-diameter fiber grating, and the deformation of the second etched stepped reduced-diameter fiber grating is a half of the deformation of the first etched stepped reduced-diameter fiber grating; the second etched stepped reduced-diameter fiber grating undergoes a deformation of an equal magnitude and the same direction as that of the third etched stepped reduced-diameter fiber grating,
ε
Fx
2
=
ε
Fx
3
=
-
ε
Fx
1
2
is met, where ε Fx1 is the deformation that occurs to the first etched stepped reduced-diameter fiber grating, ε Fx2 is the deformation that occurs to the second etched stepped reduced-diameter fiber grating, and ε Fx3 is the deformation that occurs to the third etched stepped reduced-diameter fiber grating; thus, when the elastomer ( 2 ) is only subjected to the action of the axial force F X , wavelength drifts corresponding to the normal sections and the etched stepped reduced-diameter sections of the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) are:
{
Δ
λ
1
-
n
=
c
1
+
C
λ
1
-
n
(
1
-
P
e
)
ε
Fx
1
=
K
x
1
-
n
Δ
λ
1
-
e
=
1
1
+
C
λ
1
-
c
(
1
-
P
e
)
ε
Fx
1
=
K
x
1
-
e
Δ
λ
2
-
n
=
c
(
1
+
C
)
λ
2
-
n
(
1
-
P
e
)
ε
Fx
2
=
K
x
2
-
n
Δ
λ
2
-
e
=
1
(
1
+
C
)
λ
2
-
e
(
1
-
P
e
)
ε
Fx
2
=
K
x
2
-
e
Δ
λ
3
-
n
=
c
(
1
+
C
)
λ
3
-
n
(
1
-
P
c
)
ε
Fx
3
=
K
x
3
-
n
Δ
λ
3
-
e
=
1
(
1
+
C
)
λ
3
-
e
(
1
-
P
e
)
E
Fx
3
=
K
x
3
-
e
,
where K xi-n and K xi-e are force sensitivities of the normal section and the etched stepped reduced-diameter section of the etched stepped reduced-diameter fiber grating ( 7 ) when the elastomer ( 2 ) is only subjected to the action of the transverse force F X ;
when the three-dimensional force sensor is only subjected to action of the longitudinal force F y , the elastomer ( 2 ) undergoes a longitudinal deformation, the first etched stepped reduced-diameter fiber grating is located on a neutral layer, the second etched stepped reduced-diameter fiber grating undergoes a deformation of an equal magnitude and an opposite direction to the third etched stepped reduced-diameter fiber grating, such that deformations of the second etched stepped reduced-diameter fiber grating and the third etched stepped reduced-diameter fiber grating are ε Fy2 and ε Fy3 when the longitudinal force F y acts, then when the elastomer ( 2 ) is only subjected to the action of the longitudinal force F y , wavelength drifts corresponding to the normal sections and the etched stepped reduced-diameter sections of the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) are:
{
Δ
λ
1
-
n
=
0
Δ
λ
1
-
e
=
0
Δ
λ
2
-
n
=
c
(
1
+
C
)
λ
2
-
n
(
1
-
P
e
)
ε
Fy
2
=
K
y
2
-
n
Δ
λ
2
-
e
=
1
(
1
+
C
)
λ
2
-
e
(
1
-
P
e
)
ε
Fy
2
=
K
y
2
-
e
Δ
λ
3
-
n
=
c
(
1
+
C
)
λ
3
-
n
(
1
-
P
e
)
ε
Fy
3
=
K
y
3
-
n
Δ
λ
3
-
e
=
1
(
1
+
C
)
λ
3
-
e
(
1
-
P
e
)
ε
Fx
3
=
K
y
3
-
e
}
,
where K yi-n and K yi-e are force sensitivities of the normal section and the etched stepped reduced-diameter section of the etched stepped reduced-diameter fiber grating ( 7 ) when the elastomer ( 2 ) is only subjected to the action of the longitudinal force F y ;
when an ambient temperature changes, a central wavelength of the optical fiber drifts due to a thermo-optic effect of the optical fiber, a thermal expansion effect, and an elastic-optic effect caused by an internal thermal stress, and wavelength drifts corresponding to the normal sections and the etched stepped reduced-diameter sections of the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) under an influence of the temperature are:
{
Δ
λ
t
1
-
n
=
C
T
λ
1
-
n
Δ
T
=
K
T
1
-
n
Δ
λ
t
1
-
e
=
C
T
λ
1
-
e
Δ
T
=
K
T
1
-
e
Δ
λ
t
2
-
n
=
C
T
λ
2
-
n
Δ
T
=
K
T
2
-
n
Δ
λ
t
2
-
e
=
C
T
λ
2
-
e
Δ
T
=
K
T
2
-
e
Δ
λ
t
3
-
n
=
C
T
λ
3
-
n
Δ
T
=
K
T
3
-
n
Δ
λ
t
3
-
e
=
C
T
λ
3
-
e
Δ
T
=
K
T
3
-
e
,
where Δλ ti-n and Δλ ti-e are the wavelength drifts of the normal sections and the etched stepped reduced-diameter sections of the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) under action of the temperature; a relative temperature sensitivity coefficient of the etched stepped reduced-diameter fiber grating ( 7 ) is C T =ζ+σ, ζ is a thermo-optic coefficient of the etched stepped reduced-diameter fiber grating ( 7 ), and o is a linear thermal expansion coefficient of the etched stepped reduced-diameter fiber grating ( 7 ); K Ti-n and K Ti-e are temperature sensitivities of the normal section and the etched stepped reduced-diameter section of each etched stepped reduced-diameter fiber grating ( 7 ) respectively when the elastomer ( 2 ) is only subjected to the influence of the temperature; and
synthesizing the above cases where the force and the temperature act separately, a relationship matrix of the central wavelength drift amounts of reflectance spectra of the three groups of etched stepped reduced-diameter fiber gratings ( 7 ) and the three-dimensional force as well as the temperature is obtained as:
[
Δ
λ
1
‐
n
Δ
λ
1
‐
e
Δ
λ
2
‐
n
Δ
λ
2
‐
e
Δ
λ
3
‐
n
Δ
λ
3
-
e
]
=
Δλ
6
×
1
=
K
6
×
4
[
F
x
F
y
F
z
Δ
T
]
=
[
K
x
1
‐
n
0
K
z
1
‐
n
K
T
1
‐
n
K
x
1
‐
e
0
K
z
1
‐
e
K
T
1
‐
e
K
x
2
‐
n
K
y
2
‐
n
K
z
2
‐
n
K
T
2
‐
n
K
x
2
‐
e
K
y
2
‐
e
K
z
2
‐
e
K
T
2
‐
e
K
x
3
‐
n
K
y
3
‐
n
K
z
3
‐
n
K
T
3
‐
n
K
x
3
-
e
K
y
3
-
e
K
z
3
-
e
K
T
3
-
e
]
[
F
x
F
y
F
z
Δ
T
]
,
where Δλ 6×1 is a central wavelength drift amount of the normal section and the etched stepped reduced-diameter section of each etched stepped reduced-diameter fiber grating ( 7 ), and K 6×4 is the force and temperature sensitivity matrix.
6 . The method for detecting the three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing according to claim 5 , wherein a content of step S 3 is: solving the three-dimensional force and the temperature
[
F
x
F
y
F
z
Δ
T
]
=
C
4
×
6
·
Δλ
6
×
1
by solving the generalized inverse matrix C 4×6 of the sensitivity matrix K 6×4 as the calibration matrix, and through the central wavelength drift amount Δλ 6×1 of the normal section and the etched stepped reduced-diameter section of each etched stepped reduced-diameter fiber grating ( 7 ).
7 . The method for detecting the three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing according to claim 6 , wherein The content of step S 4 is: using a Kalman filtering method to filter the historically measured three-dimensional force time series data of the three-dimensional force sensor, and normalizing the filtered three-dimensional force time series data; dividing the normalized three-dimensional force time series data into a training set and a test set, wherein the training set is used to establish a model, and the test set is used to verify a generalization ability of the model; and using a sliding time window to construct the training sample, building an LSTM neural network model, and using the training set to train parameters of the LSTM neural network model.
8 . The method for detecting the three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing according to claim 7 , wherein a content of step S 5 is: using the random forest algorithm to classify the tissues clamped by the clamp head ( 1 ), using the three-dimensional force obtained from a decoupling calculation as an input set of the random forest algorithm, using the types of the tissues as outputs, setting, in a training process of the random forest algorithm, the number of decision trees to be 100, a minimum number of leaves to be 1, and the number of candidate features for feature selection for each tree to be 2, using 70% of the input set as the training set, and using remaining 30% of the input set as the test set to verify the trained random forest algorithm.
9 . The method for detecting the three-dimensional force of a fiber-integrated monolithic clamp guided by metal additive manufacturing according to claim 3 , wherein a diameter of the etched stepped reduced-diameter fiber grating ( 7 ) is 125 μm, a length of the grating region is 3 mm, and the normal section and the etched stepped reduced-diameter section each contain a half of the grating region.