Optical stress sensing system with directional measurement capabilities
First Claim
1. An optical sensing system for measuring applied stress, comprising:
- a sensing element comprising a monolithic isotropic material exhibiting stress induced birefringence;
means for establishing a first polarized light beam along a first optical path through the sensing element having a first known directional sensitivity to applied stress;
means for establishing a second polarized light beam along a second optical path through the sensing element having a second known directional sensitivity to applied stress;
means for establishing a third polarized light beam along a third optical path through the sensing element having a third known directional sensitivity to applied stress;
measuring means for measuring an optical response of each of the first, second, and third optical paths to applied stress; and
determining means, responsive to the measuring means, for determining a magnitude and a direction of the applied stress.
1 Assignment
0 Petitions
Accused Products
Abstract
A stress sensor having directional measurement capabilities based on the photoelastic effect in isotropic photoelastic materials. Directional measurement capability is achieved in the sensor by the incorporation of three different optical axes passing through the photoelastic element. This creates three independent stress sensors which utilize a single sensing element. Each of the three independent stress sensors are sensitive to applied stress in different directions. The response of each of the sensors is analyzed and the magnitude and direction of incoming stress is determined. The use of a sum-difference output detection scheme results in immunity to light source intensity variations, optical fiber microbending losses, and fiberoptic connector losses. The stress sensor is immune to electromagnetic interference (EMI) and electromagnetic pulse (EMP), and is compatible with fiberoptic data transmission and control lines.
57 Citations
24 Claims
-
1. An optical sensing system for measuring applied stress, comprising:
-
a sensing element comprising a monolithic isotropic material exhibiting stress induced birefringence; means for establishing a first polarized light beam along a first optical path through the sensing element having a first known directional sensitivity to applied stress; means for establishing a second polarized light beam along a second optical path through the sensing element having a second known directional sensitivity to applied stress; means for establishing a third polarized light beam along a third optical path through the sensing element having a third known directional sensitivity to applied stress; measuring means for measuring an optical response of each of the first, second, and third optical paths to applied stress; and determining means, responsive to the measuring means, for determining a magnitude and a direction of the applied stress. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
-
-
15. An optical stress sensing system for measuring applied stress, comprising:
-
a sensing element including a monolithic isotropic photoelastic material; means for establishing a first polarized light beam along a first optical path through the sensing element to transmit light from a light source; means for establishing a second polarized light beam along a second optical path through the sensing element to transmit light from a light source; means for establishing a third polarized light beam along a third optical path through the sensing element to transmit light from a light source; means for measuring a sum difference optical output from each of the first, second, and third optical paths; and means, responsive to the measuring means, for determining a magnitude and a direction of the applied stress. - View Dependent Claims (16, 17, 18)
-
-
19. In a stress sensing system having at least three sensors respectively having known directional sensitivity to applied stress, a method for determining a magnitude and direction of the applied stress comprising the steps of:
-
detecting the individual optical outputs for each sensor; calculating a sum-difference output for each sensor; and determining, from the calculated sum-difference for each sensor, a magnitude and direction of the applied stress. - View Dependent Claims (20, 21)
-
21. The method of claim 19, wherein the determining step includes solving a system of equations including:
-
space="preserve" listing-type="equation">SD.sub.1 =[SIN Γ
(S)][(COS.sup.2 θ
-(SIN.sup.2 φ
SIN.sup.2 θ
)]
space="preserve" listing-type="equation">SD.sub.2 =[SIN Γ
(S)][SIN2θ
SINφ
]
space="preserve" listing-type="equation">SD.sub.3 =[SIN Γ
(S)][SIN2θ
COSφ
]where; SD1 =measured sum-difference output for the first optical path SD2 =measured sum-difference output for the second optical path SD3 =measured sum-difference output for the third optical path SIN (Γ
(S))=stress induced birefringence amplitudeφ
=the angle from the X-axis in the X-Y planeθ
=the angle with the Z-axis.
-
-
-
22. An optical stress sensing system for measuring applied stress, comprising:
-
a planar stress sensing element comprising a monolithic isotropic material exhibiting stress induced birefringence; a first optical stress sensor having a first light path through the sensing element for transmitting light polarized along a first plane and having a first known directional sensitivity to applied stress; a second optical stress sensor having a second light path through the sensing element for transmitting light polarized along a second plane and having a second known directional sensitivity to applied stress; a third optical stress sensor having a third light path through the sensing element for transmitting light polarized along a third plane and having a third known directional sensitivity to applied stress; a light measuring device for detecting a change in light transmission in each of the three optical paths; and a calculator for calculating a magnitude and direction of the applied stress as a function of the change in light transmission measured by the light measuring device. - View Dependent Claims (23, 24)
-
Specification