Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Patent
1997-12-16
2000-01-25
Noori, Max
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
G01L 124
Patent
active
060167092
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a pressure-sensitive optical device and to a presence-detection floor including the optical device.
Optical devices are known that serve to measure a pressure by sensing the attenuation in the intensity of light transmitted by an optical fiber, said attenuation being caused by the fiber deforming when it is subjected to a force.
In particular, document FR-A-2 578 645 discloses a pressure-sensitive optical cloth in which deformation of the measurement optical fiber is induced by external elements constituted by fibers disposed perpendicularly to the measurement fiber and on opposite sides thereof. Also, document EP-A-419 267 discloses a pressure-sensitive optical device in which the deformation of the optical fiber is induced by rigid external elements, e.g. layers or plates that are corrugated or of sawtooth shape.
Those devices suffer from the major drawback of giving rise to permanent friction of the external elements against the surface of the fiber. That leads rapidly to the surface of the fiber being spoilt, which gives rise to permanent modification of the light signal transmitted by the fiber, and even to the fiber breaking.
For devices that are used for safety or security purposes, e.g. to detect the presence of an employee in a dangerous zone, or the presence of an intruder in a building, the light signal transmitted to the sensor after passing along the fiber must be reproducible, in order to avoid triggering false alarms while also being certain to respond under the intended conditions.
In order to mitigate the above-mentioned drawbacks, the invention proposes a pressure-sensitive device comprising a series of measurement optical fiber segments and a series of stress members, such that stress fiber segments extend transversely to a longitudinal direction of the measurement optical fiber segments, the stress members being disposed alternately on opposite sides of the measurement optical fiber segments, and in which the measurement optical fiber segments and/or the stress fiber segments are covered in a protective member disposed to allow the fiber segments it covers to move relative to the protective member.
Thus, the force applied to the stress members and transmitted to the measurement optical fiber is spread by the protective member so that dry friction between the measurement optical fiber segments and the stress members is softened and the wear zone is enlarged, thereby minimizing wear of the measurement optical fiber, and where appropriate of the stress fiber segments, and considerably increasing the lifetime of the pressure-sensitive device. In addition, the fiber segments are also protected during manufacture of the device.
In an advantageous version of the invention, the protective member is constituted by at least one thread that is helically wound, braided, knitted, or woven. This provides a sheath that is easily deformable and that has sufficient freedom of movement.
Preferably, the sheath is then made with a thread of material that is softer than the fiber which it protects. Thus, the wear which results from friction applies mainly to the sheath, thereby correspondingly extending the lifetime of the measurement optical fiber.
According to an advantageous feature of the invention, the sheath is made with a thread that is small in diameter compared with the diameter of the fibers it covers. This minimizes the increase in the diameter of the fiber segments and consequently the bending stresses to which the measurement optical fiber is subjected when the device is subjected to pressure.
According to another advantageous feature of the invention, the measurement optical fiber is a silica fiber and the stress fiber is made of synthetic material. This provides a good compromise between performance and cost.
In another aspect, the invention provides a presence-detection floor including a pressure-sensitive device of the invention disposed between a top layer of resilient material and a bottom layer of resilient material, a flexible metal sheet being disposed
REFERENCES:
patent: 4781056 (1988-11-01), Noel et al.
patent: 4836030 (1989-06-01), Martin
patent: 4947693 (1990-08-01), Szuchy et al.
patent: 5029977 (1991-07-01), Wheeler et al.
patent: 5309767 (1994-05-01), Parmar et al.
patent: 5357813 (1994-10-01), Weinberger
Carnicelli Vito
Gierczak Marek
Godfroy Dominique
Fredrick Kris T.
Honeywell Inc.
Noori Max
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