US 9,176,015 B1Granted

Point load sensor

AssigneeThe United States of America as represented by the Secretary of the Navy

InventorJeffrey K. Sefranek

Life of this patent

Estimating the term…

Abstract

A point load sensor measures compressive forces exerted on the outside of a ring in diametric compression irrespective of the direction of application of the force. The sensor consists of a ring with strain gauges placed in a configuration to measure the circumferential strain at two positions on the ring ninety degrees apart resulting from bending of the ring as the ring is loaded in diametric compression. The two measurements are corrected and combined to recover the compressive force on the ring. A method for calibrating and resolving the compressive force does not require the angle of loading or sensor orientation as an input, thus allowing resolution irrespective of the direction of the compressive force.

Claims1

Dependent claims

A method for calibrating a sensor ring by measuring a diametric compressive force on the sensor ring, said method comprising the steps of:

applying a known compressive load, PK, at a plurality of orientations about the sensor ring such that the sensor ring is placed in diametric compression and there will be a bending moment through a thickness of the sensor ring from applying the load;
for each of the orientations about the ring, measuring a first output voltage, VA, resulting from the bending moment, across first output connections from a first gauge of a first pair of strain gauges and from a second gauge of the first pair of gauges with the second gauge spaced apart one hundred and eighty degrees circumferentially on an interior of the ring;
for each of the orientations about the sensor ring, measuring a second output voltage, VB, resulting from the bending moment, across second output connections from a first gauge of a second pair of strain gauges spaced ninety degrees apart circumferentially on the interior of the ring apart from the first gauge of the first pair of strain gauges, and from a second gauge of the second pair of strain gauges in which the second gauge of the second pair is spaced one hundred and eighty degrees apart from the first gauge of the second pair, the output voltages forming a set of paired first and second output voltages for the plurality of orientations;
initializing values of 1 for correction slopes mA and mB;
initializing values of 0 for offsets bA and bB;
for the set of paired output voltages, calculating a corresponding set of parameters, V1 and V2, based on respective relationships V1=mAVA+bA and V2=mBVB+bB;
for the corresponding set of parameters, V1 and V2, calculating a set of uncorrected loads, UP to recover a point load directly, based on the relationship
UP
=
-
(
4
⁢
(
V
1
+
V
2
)
π
)
+
16
π
2
⁢
(
V
1
+
V
2
)
2
-
4
⁢
(
8
-
π
2
π
2
)
⁢
(
V
1
2
+
V
2
2
)
2
⁢
(
8
-
π
2
π
2
)
;
obtaining a standard deviation for the set of uncorrected loads;
iteratively varying values for at least one of mA, mB, bA and bB and returning to calculating corresponding sets of parameters, V1 and V2, sets of uncorrected loads, UP, and standard deviations;
minimizing, based on said iteration step, the standard deviations where A, B and C are constants based on the relationship
UP=A(V1+V2)+√{right arrow over (B(V1+V2)2−C(V12+V22))}{right arrow over (B(V1+V2)2−C(V12+V22))}
selecting final values for mA, mB, bA and bB, based on said step of minimizing the standard deviation step;
selecting final values representing the least standard deviation for coefficients A, B and C based on said minimizing of the standard deviation step;
iteratively varying load PK;
returning to applying load PK to obtain a set of PK versus UP values;
determining a best fit curve for the set of PK versus UP values based on Pk=M*UP+Y where M is the designated slope and Y is the designated offset;
calibrating the sensor ring for independent load analysis as a reference standard based on positioning orientation;
and
calibrating the sensor ring output based on deviations from linearity.

76 more elements

Dependencies are inferred from the claim text.

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Abstract

A method for calibrating a sensor ring by measuring a diametric compressive force on the sensor ring, said method comprising the steps of:

applying a known compressive load, PK, at a plurality of orientations about the sensor ring such that the sensor ring is placed in diametric compression and there will be a bending moment through a thickness of the sensor ring from applying the load;
for each of the orientations about the ring, measuring a first output voltage, VA, resulting from the bending moment, across first output connections from a first gauge of a first pair of strain gauges and from a second gauge of the first pair of gauges with the second gauge spaced apart one hundred and eighty degrees circumferentially on an interior of the ring;
for each of the orientations about the sensor ring, measuring a second output voltage, VB, resulting from the bending moment, across second output connections from a first gauge of a second pair of strain gauges spaced ninety degrees apart circumferentially on the interior of the ring apart from the first gauge of the first pair of strain gauges, and from a second gauge of the second pair of strain gauges in which the second gauge of the second pair is spaced one hundred and eighty degrees apart from the first gauge of the second pair, the output voltages forming a set of paired first and second output voltages for the plurality of orientations;
initializing values of 1 for correction slopes mA and mB;
initializing values of 0 for offsets bA and bB;
for the set of paired output voltages, calculating a corresponding set of parameters, V1 and V2, based on respective relationships V1=mAVA+bA and V2=mBVB+bB;
for the corresponding set of parameters, V1 and V2, calculating a set of uncorrected loads, UP to recover a point load directly, based on the relationship
UP
=
-
(
4
⁢
(
V
1
+
V
2
)
π
)
+
16
π
2
⁢
(
V
1
+
V
2
)
2
-
4
⁢
(
8
-
π
2
π
2
)
⁢
(
V
1
2
+
V
2
2
)
2
⁢
(
8
-
π
2
π
2
)
;
obtaining a standard deviation for the set of uncorrected loads;
iteratively varying values for at least one of mA, mB, bA and bB and returning to calculating corresponding sets of parameters, V1 and V2, sets of uncorrected loads, UP, and standard deviations;
minimizing, based on said iteration step, the standard deviations where A, B and C are constants based on the relationship
UP=A(V1+V2)+√{right arrow over (B(V1+V2)2−C(V12+V22))}{right arrow over (B(V1+V2)2−C(V12+V22))}
selecting final values for mA, mB, bA and bB, based on said step of minimizing the standard deviation step;
selecting final values representing the least standard deviation for coefficients A, B and C based on said minimizing of the standard deviation step;
iteratively varying load PK;
returning to applying load PK to obtain a set of PK versus UP values;
determining a best fit curve for the set of PK versus UP values based on Pk=M*UP+Y where M is the designated slope and Y is the designated offset;
calibrating the sensor ring for independent load analysis as a reference standard based on positioning orientation;
and
calibrating the sensor ring output based on deviations from linearity.

76 more elements