Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L1/00—Measuring force or stress, in general
  • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
  • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
  • G01L1/243—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis
  • G01L1/245—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis using microbending
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/02—Mechanical actuation
  • G08B13/10—Mechanical actuation by pressure on floors, floor coverings, stair treads, counters, or tills

Definitions

• the present invention relates to an optical device sensitive to pressure and to a presence detection floor comprising this optical device.
• Optical devices which make it possible to measure a pressure by capturing the attenuation of the light intensity transmitted by an optical fiber, this attenuation being caused by the deformation of the fiber when the latter is subjected to a force.
• Document FR-A is known in particular
• 2,578,645 a pressure-sensitive optical fabric in which the deformations of the measuring optical fiber are caused by external elements constituted by fibers arranged perpendicular to the measuring fiber on either side thereof.
• Document EP-A-419 267 also discloses an optical device sensitive to pressure in which the deformations of the optical fiber are induced by rigid external elements, for example sheets or sheets corrugated or sawtooth.
• the light signal transmitted to the sensor after passing through the fiber must be reproducible so as not to trigger an undue alarm but also to react with certainty under the conditions provided.
• a device sensitive to the pressure comprising a series of measuring optical fiber segments and a series of constraining members, such as stressing fiber segments extending transversely to a longitudinal direction of the measuring optical fiber segments, the constraining members being arranged alternately on either side of the measuring optical fiber segments, in which the measuring optical fiber segments and / or the stressed fiber segments are covered with a protective member arranged to allow movement relative to the protection member with respect to the segment of fiber which it covers.
• the force applied to the constraining members and transmitted to the optical measuring fiber is distributed by the protective member so that the dry friction between the segments of optical measuring fiber and the constraining members is softened and the wear zone is widened, which minimizes the wear of the measuring optical fiber, and if necessary of the stress fiber segments, and considerably increases the service life of the pressure-sensitive device.
• protection of the fiber segments is also ensured during the manufacture of the device.
• the protective member consists of at least one gimped, knitted, braided or woven thread. This gives an easily deformable sheath and having sufficient freedom of displacement.
• the sheath is then produced with a wire of softer material than the fiber which it protects.
• the wear resulting from friction is mainly supported by the sheath, which consequently extends the service life of the measuring optical fiber.
• the sheath is produced with a wire having a small diameter compared to that of the fibers which it covers. We minimize thus the increase in diameter of the fiber segments and consequently the curvature stress to which the measuring optical fiber is subjected when the device is subjected to a pressure.
• the optical measurement fiber is made of silica and the strain fiber is made of synthetic material. This achieves a good compromise between performance and cost.
• this relates to a presence detection floor comprising a pressure-sensitive device according to the invention disposed between a layer of upper elastic material and a layer of lower elastic material, a flexible metal sheet being disposed above the upper elastic material layer.
• FIG. 2 is an enlarged sectional view along the line II-II of FIG. 1, of a detection floor equipped with a pressure-sensitive fabric according to the invention, in the rest position,
• Figure 3 is a view similar to that of Figure 2 of a detection floor subjected to a load.
• the optical tissue sensitive to pressure comprises an optical measuring fiber generally designated at 2, arranged along meanders comprising a series of rectilinear measuring optical fiber segments 2a, 2b, 2c parallel.
• the pressure-sensitive optical fabric Perpendicular to the measuring optical fiber segments, the pressure-sensitive optical fabric comprises stress fiber segments generally designated at 3, arranged alternately on either side of the measuring optical fiber segments 2.
• the segments arranged above the measurement optical fiber 2 have been denoted by the reference numeral 3a while the segments disposed below the measurement optical fiber bear the reference numeral 3b.
• the spacing between the rectilinear segments of the measuring optical fiber must be sufficient to avoid loss of light signal resulting from the curvature of the measuring optical fiber between the rectilinear segments. In practice, a distance of about 50 mm has proven to be very satisfactory. Furthermore, to ensure satisfactory attenuation of the light signal in the measurement optical fiber during the application of a force on the stress fiber segments, these segments are arranged in a manner known per se at a pitch equal to a multiple of the half-wavelength of light propagation in the fiber used. In practice, a pitch of the order of 3.5 mm has proven to be very satisfactory.
• the measuring fiber optics and the stress fiber segments are produced from the same optical fiber with an index gradient of doped silica / silica / methacrylate-coated acrylate , with dimensions 50 ⁇ m / 125 ⁇ m / 250 ⁇ m, and digital aperture 0.2.
• the fiber segments are covered with a protective member arranged to allow relative movement of the protective member and the covered fiber segments.
• the protection consists of a sheath formed of a polyamide 4 multifilament with a diameter close to 50 ⁇ m wound helically around the fiber segments to form a covering thereof.
• the constraint fibers 3 being incorporated into the fabric in the form warp yarn while the measuring optical fiber is incorporated into the retaining fabric 4 in the form of weft yarn.
• a stress fiber segment 3a of the upper ply constitutes with two stress fiber segments 3b of the lower ply a stress node 6.
• the stress fiber 3a a constraint node tends to move to be inserted between the fibers 3b of the same node and causes a deformation of the measuring optical fiber segment 2.
• Several adjacent constraint nodes 6 thus cause a sinusoidal or pseudosinusoidal deformation of the optical fiber of measure 2 and it was found that from three constraint nodes adjacent the light attenuation caused by a charge was sufficient to be detected by means of simple electronic devices.
• a homogeneous distribution of the stress fiber segments would lead to an equally homogeneous distribution of the pressure applied to a large number of stress nodes so that the bending of the optical fiber would risk being below a threshold necessary to cause a perceptible attenuation of the light in the optical measurement fiber.
• a group of stress fiber segments will preferably have seven to eleven stress fiber segments making three to five adjacent stress nodes.
• Two groups of strain fibers 7 are spaced apart by a distance suitable for the use of the pressure-sensitive mat.
• the groups of stress fibers will be spaced at a distance less than the dimension of a foot so that it is not possible to lay a foot on the pressure-sensitive mat without causing the compression of at least one group of constraint nodes.
• a pattern of groups of stress fibers repeating is produced approximately every 50 mm.
• the retaining fabric 5 has the function not only of maintaining the measuring optical fiber segments and the stressing optical fiber segments according to the desired relative position, but also ensures a limit on the amplitude of the deformation of the optical fiber of measure 2 by making a stop for the optical fiber of measure 2 when the stress fibers move towards one another under the effect of pressure. This prevents a segment of stress fiber of the upper layer from fully penetrating between the segments of stress fiber of the lower layer, which would cause an excessively pronounced curvature of the optical fiber 2 and would risk causing the rupture of this one.
• the pressure-sensitive fabric according to the invention is preferably used by incorporating it into a presence detection floor 8 comprising for example a layer of cellular foam 9 with closed cells having for function of isolating floor 8 from the ground and absorbing roughness and gravel.
• a foam layer of about 3mm is sufficient to perform this function.
• the presence detection floor comprises two protective elastomer layers 10 and 11 having a thickness of between 1.5 and 2 mm, which frame the pressure-sensitive fabric.
• a flexible metal sheet 12 is preferably arranged above the protective elastomer layer 11.
• the metal sheet 12 has a high elastic limit and serves to protect the pressure-sensitive mat by distributing the pressure of an applied load so too punctual on the pressure sensitive mat.
• the metal sheet 12 is preferably covered with an elastomeric coating 13 having a non-slip function, and absorbing the accidental fall of an object.
• One end of the measuring optical fiber 2 is connected in a manner known per se to a light source while the other end is connected to an electronic device for detecting light attenuation.
• the light source and the detection device can also be placed at the same end of the measuring optical fiber 2 by using a light separator at this end and by placing a mirror at the opposite end of the measuring optical fiber 2 so as to to return the light emitted.
• This arrangement ensures a double passage of the light in the optical measurement fiber and therefore ensures a doubling of the detection dynamics without however causing modal recombinations.
• the losses recorded are then twice as large, which allows greater reliability of the mat, which thus proves to be particularly useful in a safety device.
• the protective member 4 has been illustrated by a covering, it can also be produced by a knitted, braided or woven wire, or even by an extruded sheath having an internal diameter very slightly greater than the external diameter covered fiber to allow relative movement of the protective member and covered fiber segments.
• the retaining mat has been illustrated with threads extending between the stress fiber segments, it is also possible to use a retaining fabric, the fibers of which cover the stress fibers.
• the pressure-sensitive device according to the invention can also be produced by covering only one of the series of fiber segments, or by using stress fiber segments of a different nature from the measuring optical fiber. It is also possible to produce a pressure-sensitive device associating an optical measurement fiber with stress members of different material, for example corrugated plates or comprising sawtooth ribs. In this case, the measuring optical fiber will be wrapped.
• the measuring optical fiber 2 is continuous, the straight segments 2a, 2b, 2c being joined by curved parts, it is possible to provide a pressure-sensitive mat comprising several segments of measuring optical fibers separated, each connected to a light source and a detection device. It is also possible to provide for a pressure-sensitive fabric in which the stress fiber segments are not exactly perpendicular to the measurement optical fiber segments, for example a fabric comprising a spiral measurement optical fiber and segments of stress fiber arranged substantially radially.
• the measuring optical fiber and the stress fiber are both silica fibers which give very good results due to the low hysteresis of the silica fiber, it turns out that that -This is very expensive and we can achieve a good compromise between cost and performance by using a synthetic fiber constraint, for example fishing line.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Light Guides In General And Applications Therefor (AREA)
• Force Measurement Appropriate To Specific Purposes (AREA)
• Measuring Fluid Pressure (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 1995
  • 1995-04-26 FR FR9504986A patent/FR2733591B1/fr not_active Expired - Fee Related
• 1996
  • 1996-03-22 WO PCT/FR1996/000436 patent/WO1996034262A1/fr not_active Ceased
  • 1996-03-22 JP JP53220896A patent/JP3920334B2/ja not_active Expired - Fee Related
  • 1996-03-22 US US08/945,127 patent/US6016709A/en not_active Expired - Lifetime
  • 1996-03-22 EP EP96908175A patent/EP0823044A1/de not_active Withdrawn

Non-Patent Citations (1)

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