Resistive-capacitive deformation sensor
A deformation sensing apparatus comprises an elastic substrate, a first strain-gauge element formed on a first surface of the elastic substrate, and configured to output a first signal in response to a strain applied in a first direction, and a second strain-gauge element formed on a second surface of the elastic substrate opposite to the first surface, and configured to output a second signal in response to a strain applied in the same first direction.
1. A deformation sensing apparatus comprising:
a substrate;
a first strain-gauge element coupled to a first portion of the substrate, and configured to output a first signal in response to a strain applied in a first direction; and
a second strain-gauge element coupled to a second portion of the substrate distinct from the first portion, and configured to output a second signal in response to a strain applied in the same first direction, and
wherein the deformation sensing apparatus is further configured to output a third signal responsive to an applied deformation, the third signal being measureable between a terminal of the first strain-gauge element and a terminal of the second strain gauge-element.
2. The deformation sensing apparatus of claim 1 , wherein the first portion of the substrate is opposite to the second portion of the substrate.
3. The deformation sensing apparatus of claim 1 , wherein the first portion of the substrate is a top portion of the substrate and the second portion of the substrate is a bottom portion of the substrate.
4. The deformation sensing apparatus of claim 1 , wherein:
the first strain-gauge element has two distinct terminals, a first terminal and a second terminal;
the first signal is measurable across the first and second terminals of the first strain-gauge element;
the second strain-gauge element has two distinct terminals, a third terminal and a fourth terminal; and
the second signal is measurable across the third and fourth terminals of the second strain-gauge element.
5. The deformation sensing apparatus of claim 1 , wherein the substrate comprises a flexible, electrically-insulating dielectric material.
6. The deformation sensing apparatus of claim 5 , wherein:
each of the first and second strain-gauge elements has a horse-shoe shape comprising an arcuate head and a pair of elongate leads extending from ends of the arcuate head;
alignment of the shapes of the first and second strain-gauge elements correspond along an axis orthogonal to the first portion and the second portion of the substrate;
central axes of the first and second strain-gauge elements are aligned parallel and coplanar to each other along a planes orthogonal to the first portion and the second portion of the substrate; and
corresponding leads of the pairs of elongate leads of the first and second strain-gauge elements are respectively length-wise parallel and have substantially the same dimensions.
7. The deformation sensing apparatus of claim 6 , wherein:
a measurement circuit configured to measure the first signal from the first strain-gauge element and the second signal from the second strain-gauge element in response to an applied deformation; and
a deformation analyzer configured to compute a measure of stretch deformation and a measure of flex deformation of the sensing apparatus, in the applied deformation, based on the measured first signal from the first strain-gauge element, the measured second signal of the second strain-gauge element, and the third signal.
8. The deformation sensing apparatus of claim 7 , wherein:
the measure of stretch deformation is indicative of an average change in lengths in relationship to an undeformed length of the first and second strain gauge elements; and
the measure of flex deformation is indicative of a bend radius of an angular bend of portions of the substrate on which the first and second strain-gauge elements are formed.
9. The deformation sensing apparatus of claim 7 , wherein the deformation analyzer is further configured to determine whether the stretch deformation corresponds to a compression stretch or an elongation stretch, by comparing the measured first, second, and third signals, based on a sign of changes in resistances of the first and second strain gauge elements and a sign of change in capacitance of the substrate.
10. The deformation sensing apparatus of claim 1 , further comprising:
a measurement circuit configured to measure the first signal from the first strain-gauge element and the second signal from the second strain-gauge element in response to the applied deformation; and
a deformation analyzer configured to compute a measure of stretch deformation and a measure of flex deformation of the sensing apparatus, in the applied deformation, based on the measured first signal from the first strain-gauge element, the measured second signal of the second strain-gauge element, and the third signal.
11. The deformation sensing apparatus of claim 10 , wherein:
the first signal is indicative of a first resistance of the first strain-gauge element;
the second signal is indicative of a second resistance of the second strain-gauge element; and
the third signal is indicative of a capacitance across the substrate measured responsive to the applied deformation.
12. The deformation sensing apparatus of claim 11 , wherein the deformation analyzer computes the measure of stretch deformation as a proportion of length change ((ΔL)/L 0 ) of the first and second strain-gauge elements, based on the first, second, and third signals, using the equations:
R
1
=
R
2
=
R
0
+
(
GF
·
Δ
L
)
C
=
ℰ
Area
gap
=
ℰ
=
L
0
·
W
0
g
=
ℰ
L
0
·
W
0
(
g
0
-
Δ
L
·
)
=
ℰ
L
0
·
W
0
(
g
0
-
(
Δ
L
1
+
Δ
L
2
2
)
)
,
where R 1 is the first resistance, R 2 is the second resistance, C is the capacitance, and
Area is an overlap between first and second strain-gauge elements,
GF is a Gauge Factor relating strain and resistance,
γ is a Poisson's Ratio of the substrate relating deformations between axes,
L 0 is an undeformed length of the first and second strain-gauge elements,
ΔL, ΔL 1 , ΔL 2 are length changes of the first and second strain-gauge elements,
W 0 is an undeformed length of the first and second strain-gauge elements,
ε is a dielectric constant of the substrate,
R 0 is a baseline resistance of the first and second strain-gauge elements, and
g, g 0 are, respectively, deformed and baseline widths of the substrate.
13. The deformation sensing apparatus of claim 11 , wherein the deformation analyzer computes the measure of flex deformation as bend radii of the first and second strain-gauge elements, based on the first, second, and third signals, using the equations:
R
1
=
R
0
+
(
GF
·
Δ
L
1
)
≈
R
0
+
(
g
2
ρ
1
·
GF
)
R
2
=
R
0
+
(
GF
·
Δ
L
2
)
≈
R
0
+
(
-
g
2
ρ
2
·
GF
)
,
where R 1 is the first resistance, R 2 is the second resistance, and
GF is a Gauge Factor relating strain and resistance of the first and second strain-gauge elements,
γ is a Poisson's Ratio of the substrate relating deformations between axes,
L 0 is an undeformed length of the first and second strain-gauge elements,
ΔL 1 , ΔL 2 are length changes of the first and second strain-gauge elements,
R 0 is a baseline resistance of the first and second strain-gauge elements,
g, is a deformed width of the substrate, and
ρ 1 and ρ 2 are bend radii of the first portion and the second portion of the substrate.
14. A system comprising:
one or more deformation sensors, each including:
a substrate;
a first strain-gauge element coupled to first portion of the substrate, and configured to output a first signal in response to a strain applied in a first direction; and
a second strain-gauge element coupled to a second portion of the substrate opposite to the first portion, and configured to output a second signal in response to a strain applied in the same first direction,
wherein the deformation sensor is configured to output a third signal responsive to an applied deformation, the third signal being measurable between one of the first and second terminals of the first strain-gauge element and one of the third and fourth terminals of the second strain-gauge element;
a measurement circuit configured to measure the first signal from the first strain-gauge element and the second signal from the second strain-gauge element in response to the applied deformation; and
a deformation analyzer configured to compute a measure of stretch deformation and a measure of flex deformation of the sensing apparatus, in the applied deformation, based on the measured first signal from the first strain-gauge element, the measured second signal of the second strain-gauge element, and the third signal.
15. The system of claim 14 , wherein:
each of the first and second strain-gauge elements of the deformation sensor has a horse-shoe shape comprising an arcuate head and a pair of elongate leads extending from ends of the arcuate head; and
alignment of the shapes of the first and second strain-gauge elements correspond and the shapes are configured to circumscribe an articulating joint, a movement of the joint resulting in a corresponding deformation of the deformation sensor.
16. The system of claim 14 , wherein the one or more deformation sensors are included in a wearable device.
17. The system of claim 14 , wherein the one or more deformation sensors are included in a glove.
18. The system of claim 17 , wherein the one or more deformation sensors are included in a finger of the glove.
19. The system of claim 17 , wherein the one or more deformation sensors comprise a plurality of deformation sensors, each included in a different finger of the glove.
20. A method of sensing deformation of a deformation sensor, comprising, in response to an applied deformation:
measuring a first signal from a first strain-gauge element coupled to a first portion of an substrate of the deformation sensor, the first signal indicative of a resistance of the first strain-gauge element;
measuring a second signal from a second strain-gauge element coupled to a second portion of the substrate of the deformation sensor, the second signal indicative of a resistance of the second strain-gauge element;
measuring a third signal between the first strain-gauge element and the second strain-gauge element, the third signal indicative of a capacitance across the substrate measured responsive to the applied deformation; and
computing a measure of stretch deformation and a measure of flex deformation of the deformation sensor, in the applied deformation, based on the measured first signal from the first strain-gauge element, the measured second signal of the second strain-gauge element, and the third signal.