Structural monitoring sensor system

• US 6,181,841 B1
• Filed: 01/11/2000
• Issued: 01/30/2001
• Est. Priority Date: 09/14/1995
• Status: Expired due to Fees

• Current Assignee: EFS International SA
• Original Assignee: Structural Integrity Monitoring Systems, Inc. (Matech Corporation)
• Inventors: Hodge, Malcolm H.
• Primary Examiner(s): Lee, John D.
• Assistant Examiner(s): CONNELLY, MICHELLE R
• Application Number:
  US09/481,289
• Time in Patent Office: 385 Days
• Field of Search: 385/12, 385/13
• US Class Current: 385/12
• CPC Class Codes: G01B 11/16 for measuring the deformation in a solid, e.g. optical strain gauge
• CPC Class Codes: G01D 5/268 using optical fibres G01D5/28 - G01D5/38 take precedence
• CPC Class Codes: G01M 11/086 Details about the embedment of the optical fiber within the DUT
• CPC Class Codes: G01M 5/0008 of bridges
• CPC Class Codes: G01M 5/0041 by determining deflection or stress
• CPC Class Codes: G01M 5/0091 by using electromagnetic excitation or detection

Abstract

The present invention is directed to a system for continuous physical integrity monitoring of large civil structures such as bridges and high-rise buildings . . . wherein the relevant sensor data stream is generated continuously and transmitted to the data gathering location without the need for an incoming triggering signal of any kind; i.e., it is a one way transmission system. Specifically, it is a concept for an interlinked multi-parameter Early Warning Sensor system with a fill time data management capability for structures. The invention is also directed to both the system construction, with its communication capability, and also designs of specific sensors applicable to the system as a whole. As a practical example of application of the present invention to a structure, the description in this application is directed primarily towards system applications for bridge integrity early warning systems.

Claims

1. An optical sensor for detecting movement of a first element relative to a second element along a first axis, said optical sensor comprising:

(a) a light source for generating a pulse of light;

(b) an optical receiver for receiving a pulse of light;

(c) an optical coupler;

(d) a first optical conduit operatively connected to said light source and to said optical coupler,

(e) a second optical conduit operatively connected to said optical receiver and to said optical coupler;

(f) an optical encoder comprising;

(1) a reflector grid fixed to said fat element and having a plurality of evenly spaced uniform reflective surfaces emending in a first plane which is parallel to said first axis;

(2) a transmitter grid fixed to said second element and having a plurality of evenly spaced light impervious surfaces extending in a second plane which is parallel to said first plane, the spaces between said light impervious surfaces being pervious to light, the spaces between said light impervious surfaces being optically aligned with said reflective surfaces transversely of said first and second planes; and

(3) wherein one of said reflector grid and said transmitter grid having first and second substantially identical grid portions, said second grid portion being offset from said first grid portion along said first axis by a distance which is sufficient to resolve direction of movement of said first element relative to said second element by the principle of quadrature;

(g) a first optical fiber operatively connected to said optical coupler and to said transmitter grid, said first optical fiber having an end surface for transmitting a pulse of light to said reflector grid and for receiving a reflected pulse of light from said reflector grid along a second axis which is transverse to said first and second planes, the end surface of said first optical fiber being optically aligned with said first grid portion; and

(h) a second optical fiber operatively connected to said optical coupler and to said transmitter grid, said second optical fiber having an end surface for transmitting a pulse of light to said reflector grid and for receiving a reflected pulse of light from said reflector grid along a second axis which is transverse to said first and second planes, said second optical fiber being optically aligned with said second grid portion, said second optical fiber being substantially longer than said first fiber optical fiber so that the pulse of light which is reflected from said second grid portion takes longer to reach said optical detector than the pulse of light which is reflected from said first grid portion.

2. An optical sensor for detecting movement of a first element relative to a second element along a first axis, said optical sensor comprising:

(a) a light source for generating a pulse of light;

(b) an optical detector for receiving a pulse of light;

(c) an optical coupler;

(d) a first optical conduit operatively connected to said light source and to said optical coupler;

(e) a second optical conduit operatively connected to said optical detector and to said optical coupler;

(f) an optical encoder comprising;

(1) a reflector grid fixed to said first element and having a plurality of evenly spaced uniform reflective surfaces extending in a first plane which is parallel to said first axis, said reflective surfaces being the active areas of said reflector grid and the spaces between said reflective surfaces being the passive areas of said reflector grid;

(2) a transmitter grid fixed to said second element and having a plurality of evenly spaced light impervious-surfaces extending in a second plane which is parallel to said fist plane, the spaces between said light impervious surfaces being pervious to light, the spaces between said light impervious surfaces being optically aligned with said reflective sources transversely of said first and second planes along a second axis which is transverse to first axis, the spaces between said light impervious surfaces being the active areas of said transmitter grid and said light impervious surfaces being the passive areas of said transmitter grid; and

(3) wherein each active area of one of said transmitter grid and said reflector grid is substantially equal in width to each of its corresponding passive area along said first axis and each passive area of the other of said transmitter grid and said reflector grid is substantially twice as wide as its corresponding active areas along said first axis to enable a substantially baseline triggering protocol to be used for light which is reflected from said reflective surfaces; and

(g) an optical fiber operatively connected to said optical coupler and to said transmitter grid said optical fiber having and end surface for transmitting a pulse of light to said reflector grid and for receiving a reflected pulse of light from said reflector grid transversely of said first and second planes for transmission of said reflected pulse of light to said optical detector via said optical coupler.

3. An optical sensor for detecting movement of a first element relative to a second element along a first axis, said optical sensor comprising:

(a) a light source for generating a pulse of light;

(b) an optical detector for receiving a pulse of light;

(c) an optical coupler;

(d) a first optical fiber operatively connected to said light source and to said optical coupler;

(e) a second optical fiber operatively connected to said optical detector and to said optical coupler;

(f) an optical encoder comprising;

(1) a reflector grid fixed to said first element and having a plurality of evenly spaced uniform reflective surfaces extending in first plane which is parallel to said first axis, said reflective surfaces being the active areas of said reflector grid and the spaces between reflective surfaces being the passive areas of said reflector grid;

(2) a transmitter grid fixed to said second element and having a plurality of evenly spaced light impervious surfaces extending in a second plane which is parallel to said first plane, the spaces between said light impervious surfaces being pervious to light, the spaces between said light impervious surfaces being optically aligned with said reflective surfaces transversely of said first and second planes, the spaces between said light impervious surfaces being the active areas of said transmitter grid and said light impervious surfaces being the passive areas of said transmitter grid; and

(3) wherein each active area of one of said reflector grid and said transmitter grid is equal in width to each passive area therein and each active area of the other of said transmitter grid and said reflector grid is substantially less than the width of each active area of said one of said reflector grid and said transmitter grid along said first axis, the total width along said first axis of one active area and one passive area in said transmitter grid being equal to the total width of one active area and one passive area in said reflector grid; and

(g) a third optical fiber operatively connected to said optical coupler and to said transmitter grid, said third optical fiber having an end surface for transmitting a pulse of light to said reflector grid and for receiving a reflected pulse of light from said reflector grid along a second axis which is transverse to said first and second planes for transmission of said reflected pulse of light to said optical detector via said optical coupler to enable a baseline triggering protocol to be used for light which is reflected from said reflective surfaces and where no light is reflected back to said optical fiber from a pulse of light transmitted from said optical fiber for spaced distances of relative movement between said reflective grid and said transmitter grid.

4. An optical sensor as recited in claim 3, wherein the active area of one of said transmitter grid and said reflector grid is at least twice as wide as the active area of the other of said transmitter grid and said reflector grid along said first axis.

5. An optical sensor as recited in claim 3, wherein light emerges from the end surface of said third optical fiber at a range of angles from said second axis so that some of the reflected light from said pulse of light misses the end surface of said third optical fiber, wherein said reflector grid and said transmitter grid are separated by a distance which is sufficient to enable a baseline protocol to be used in which a substantially minimum value of reflected light received at said end surface triggers an on cycle in said optical receiver, and wherein reflected light received at said end surface below said value triggers an off cycle in said optical receiver, said on cycle being equal to said off cycle for a given movement of said reflector grid relative to said transmitter grid along said first axis and for a given active-area-to-passive-area ratio for the other one of said transmitter grid and said reflector grid.

6. An optical sensor as recited in claim 5, wherein the width of each active area of said transmitter grid is equal to the width of each passive area of said transmitter grid, and wherein the width of each active area of said reflector grid, expressed as W is in accordance with the following formula in which D is the distance between said transmitter grid and said reflector grid and a is the divergent angle of a pulse of light from the end surface of said third optical fiber:

W=2D.tan (a).