Note: Descriptions are shown in the official language in which they were submitted.
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TRANSVERSELY COUPLED FIBER OPTIC SENSOR FOR MEASURING AND
CLASSIFYING CONTACT AND SHAPE
Field of Invention
This invention relates to fiber optic devices, and in particular optically
sensing
and measuring contact and shape, and classifying their properties.
Background of the Invention
Prior art optical contact and shape sensor methods include detecting contact
pressures by means of frustration of internal reflection, which can take on
many
forms.
o Prior art contact sensors have been used to produce pressure contact images
by
having an external object deform a solid sheet into contact with a clear
optical layer,
the surface of the layer being illuminated by light which it reflects
internally onto a
camera. The contacting solid or intermediate sheet replaces a covering layer
of air
in a light guiding structure with the surface thereon, so that internal
reflection at the
point of contact is eliminated. In all cases, solids have a higher index than
air, so
even clear solids will tend to frustrate the reflections at the point of
contact. The
images collected by the camera or other vision system form pressure or contact
maps that can be used for tactile sensing or object recognition.
It is also known in the prior art that transmission of light through a fiber
may be
2ci frustrated by micro bending, or overbending, whereby the fiber is bent
with a
curvature sufficient to cause some of the higher modes within the fiber to
escape
through the cladding because they strike the cladding at an angle exceeding
the
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conditions for total internal reflection. An example of a microbending sensor
is given
in (Hastings, M.C. et al., "Evaluation of special communications grade fibers
in
interferometric and microbend sensors for measurements with ambient
temperature
fluctuations," SPIE Vol. 1795, Fiber Optic and Laser Sensors X, pp. 227- 235,
1992.) Microbending sensors, like the one indicated above, often use a shaped
platen to impress multiple bends in a single fiber, thereby increasing the
change in
light throughput when pressure is applied.
Sensors that detect or measure the extent of contact of a liquid are also
frequently
based on frustration of total internal reflection. Prior art liquid level
sensors include
o single point detectors that can detect presence or absence of liquid at a
discrete
point, and continuous sensors that measure the spatially continuous height of
a
liquid. Examples of prior art optical liquid level sensors include US Patent
4,038,650
to Evans, US Patent 4,353,252 to Jeans, US Patent 4,788,444 to Williams, US
Patent 4,039,845 to Oberhansli, US Patent 4,311,048 to Merz, US Patent
4,745,293
to Christensen, US Patent 3,448,616 to Wostl, US Patent 4,880,971 to Danisch,
US
Patent 5362971 McMahon, and WIPO 86/03832 to Bellhouse.
Both Evans '650 and Jeans '252 describe point detectors that rely on
frustration.
Williams '444 and Oberhansli '845 describe point detectors wherein a similar
frustration occurs within the wall of a containment. In the case of
Oberhansli, the
2o containment is the optical probe; Williams transfers the measurement to the
wall of
a clear container holding the liquid. Merz'048 uses a cylindrical rod with
circumferential V grooves to obtain a quasi- spatially continuous measurement
based on frustration at successive V grooves.
A similar approach is taken by Christensen '293, except that non-circular V's
comprise a grating, with V spacing corresponding to wavelength of the light.
Successive mode extinction is used by Wostl '616 to achieve spatially
continuous
measurement using a tapered optical rod. Danisch '971 uses a multi-layered
probe
to achieve spatially continuous measurement independent of index of refraction
of
the liquid surrounding a smooth probe. Bellhouse 86/03832 uses a loop of
optical
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fiber directly immersed in a liquid, the internal reflections being partly
frustrated by
presence of liquid where there would ordinarily be air. A loop or loops, small
enough in radius to cause egress of light, are used to increase the dependence
of
internal reflection on external media. Loops of this sort are best achieved
with
plastic optical fiber, which can be formed into tight curves without cracking.
Maximum frustration in looped sensors of this sort is achieved by removing or
disturbing the clear cladding layer on the fibers, such as by roughening with
sandpaper.
A similar looped approach is taken by McMahon '971. McMahon quantifies the
1o performance of loops of various diameters from 1/8 to over 3/8 inches in
diameter.
Water produces a loss of from 10 to 20 percent of the throughput in air, while
gasoline produces a loss of approximately 45 percent.
Examples of prior art for fiber optic shape sensing is given in Danisch
patents: US
5,321,257, US 5,633,494, WIPO 0,702,780, and PCT WO 98/41815; and
publications: Danisch, L.A., "Laminated BEAM loops," SPIE Vol. 2839, Fiber
Optic
and Laser sensors XIV, 12 pp., 1996; Danisch, L.A., Englehart, K., and
Trivett, T.,
"Spatially continuous six degree of freedom position and orientation sensor,"
Fiber
Optic and Laser Sensors and Applications, SPIE Conf. 3541A, Boston, MA, 1998;
and Danisch, L.A., "Smartmove Human Machine Interface," Volume 1 of report to
2o Canadian Space Agency, Project 9F028-7-7153/01-SW, 102 pp. + appendix, Dec.
13, 1998. In this prior art, the sensors report single degree of freedom
curvature or
complete shape using bend sensors alone, or an array of bend and twist
sensors,
respectively.
In (Danisch, L.A., "Smartmove Human Machine Interface," Volume 1 of report to
Canadian Space Agency, Project 9F028-7-7153/01-SW, 102 pp. + appendix, Dec.
13, 1998) sensor arrays are described which report complete three dimensional
shapes of an object by measuring bend and twist along a continuous flexure. In
Danisch, '257, '494, '780, and '815, sensors are described which report
monotonic
(all positive or negative) curvature as a single valued output signal. The
described
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sensors either have short sensing lengths, thereby ensuring monotonicity, or
are
long but used only in situations where monotonic curvature predominates. The
prior
art does not describe sensors designed to resolve or discriminate shape on the
basis of a single output number, other than to correlate a single number with
a net
change in angle over a long sensor length. This "averaging" is described in
Danisch,
'494, col. 19, lines 9-14: "Nevertheless, spaced emission surfaces are still
an
advantage for many sensors, as they can be used to sense average curvature
over
a greater axial length of the fiber. This can eliminate or reduce undesirable
effects
from large local changes in curvature, for instance due to the presence of a
foreign
o body under the fiber." Similar "averaging" is used in various other
commercial
devices to measure net angular changes. Examples include Penny and Giles
goniometers and Virtual Technologies Inc. instrumented gloves, both of which
use
resistive bend sensors. These sensors report net angular change at the ends of
a
long flexural sensor, without regard to the intervening shape of the sensor.
New shape sensing art introduced in the description of the present invention
includes single and double fiber sensor structures capable of generating a
distinctive, yet single-valued output which can be used to determine the class
of
shape applied. Classes of shape include curvature parameters such as
monotonic,
inflected, number of inflections, local magnitudes beyond high or low limits,
spatial
2o frequency content, and number of peaks of a given spatial frequency
content. The
new art is distinguished from the above "averaging" technique, because it does
respond to the intervening shape.
Other new shape sensing art based on double fiber structures similar to those
used
for shape classification enables improved measurement of curvature at distinct
locations, including wavelength-encoded arrays of sensors that can be used to
produce 3D measurements like those described in Danisch, 9F028-7-7153/01-SW,
cited earlier in this document, but with as few as two fibers.
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Summary of the Invention
This invention comprises sensors made from single and multiple lightguides
used as
modulators, wherein the intensity of light passing through the lightguide(s)
is
changed (modulated) by
a) external influences that change the shape of the lightguide(s), or
b) external influences that change the optical media surrounding lightguide(s)
shaped to be sensitive to contact with gases, vapors, liquids, or solids;
without necessarily further influencing the shape of the lightguide.
It can be advantageous to sense curvature or shape of a surface. This can be
useful
in sensing disturbances to civil structures, movement between parts, impacted
shape of an automobile for purposes of deploying protection devices, or as a
means
of inputting information to a computer. For occupant or pedestrian protection
device
deployment (safety system deployment), such as air bag deployment, the
deployment decision is made by an on board computer that must receive input on
the type of shape impacting. For instance, a very sharp shape, as from a
utility pole,
which might cut through the metal without activating an accelerometer used to
detect impact, is to be distinguished from a very broad shape that would be
detected
2c~ by the accelerometer. Other shapes such as multiple poles, or inflected
and non-
inflected shapes must often also be classified as part of a deployment
decision. It is
particularly important to detect shape of impact at the side of the car, where
there is
little material between the occupants and the colliding object.
For low cost shape sensing, such as for safety system deployment (e.g. air bag
CA 02307468 2000-OS-03
deployment), it is desirable to use the smallest number of sensors possible.
This
can be accomplished by classifying shapes with a small number of long,
flexible
sensors, each designed to detect a certain class or classes of shapes. The
sensors
are attached, for instance, next to each other along part of the side of the
car, such
as along a horizontal door beam. It is desired to obtain single-valued outputs
from
each sensor that can be interpreted individually to determine the class or
classes
reported by each sensor, and in concert to resolve the class of shape
impacting and
its rate of penetration. Particularly difficult classes to distinguish from
each other are
single and double sharp impacts (e.g. a utility pole vs. two small vertical
pipes). A
~o sensor that simply integrates the absolute value of curvature along its
length will
tend to report the double impact with the same output as a particularly severe
single-object impact. This is undesirable, because the two events often
require
different deployment actions. Another difficult pair of cases to distinguish
includes
broad and sharp shapes, such as those resulting from a guard rail and a
utility pole,
respectively.
It is also advantageous to know the position and weight of seat occupants in
vehicles, for purposes of automated safety system deployment. It is further
advantageous for this application to classify occupants by "configuration,"
such as
"occupant is in an infant seat with sharp edges" or "occupant is of average
weight,
2o seated in the middle of the seat". Information on these parameters can be
found by
measuring curvature or aspects of curvature, over the seat area, or chosen
portions
of the seat area.
It can also be advantageous to measure the presence, absence, and nature of
media contacting a sensor structure. The same sensors used to make shape
measurements can be made sensitive to media contact, by forming them into
particular shapes that cause some of the light travelling through them to
interact with
the surrounding media.
It has been determined that with looped plastic fibers 0.25 and 0.5 mm in
diameter,
if any clear covering layer is used to protect the loops from external media,
the
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maximum loss of light throughput that can be expected in the presence of water
is
33%, and in most cases it is in the 10-20% range. Typical coverings are clear
epoxy
or a sheet of curved material such as polyethylene or polyester. If an array
of many
looped sensors is built with such covering materials, small variations in the
thickness and integrity of contact with the covering materials will cause the
losses at
each sensor to differ greatly, so that it is difficult to process the signals
from the
loops without a calibration table. However, frequent re-calibration is
necessary
because minor contamination of the coverings by dirty films or particulates
will
change the signal levels even more than the change due to liquid replacing air
as
o the external medium. It is possible to build an array with collections of
prisms or
similar structures, but this increases its size, expense, and vulnerability to
damage
and contamination.
It can be advantageous to use an array of sensors to determine contact over a
surface or along a line, at discrete points. Such arrays can be used to
measure
height or presence of a liquid or contact of a solid. Such an array will be
most useful
if each element of the array produces a large change in signal due to contact,
and
only a minor change due to presence of contamination such as by films of oil,
dirt,
dust, or chemicals. Changes on the order of 90% due to contact will make it
unnecessary to calibrate the array, the signals being essentially binary. Yet,
even
2o though contact will be determined by essentially binary information,
readings of the
low light throughput after contact can be used to infer the nature of the
contact, such
as whether it is from a liquid of high or low optical index of refraction.
If a sensor experiences only a minor change due to contact, such as 20%, this
drop
in signal can be mimicked by a contaminant that also changes the signal by
20%,
which can occur easily. This is to be contrasted to a sensor with a throughput
which
drops to 10% in the presence of water and to 5% in the presence of oil. 20%
contamination would change these values to 8% and 4%, but they would still be
quite useable to report that a) contact had occurred and b) the type of
substance in
contact.
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The present invention enables very high modulation of light throughput due to
contact with liquids, resulting in readings that are minimally influenced by
layers of
contamination.
For most applications, whether for shape or contact sensing, it will be
necessary to
have the elements of the array protected from the surrounding media. This is
especially true if plastic fibers are used for the array. For looped arrays,
plastic
fibers are the most useful, because they can retain a sharp bend without
propagating micro-cracks and eventually failing from a condition known as
"static
~i~ fatigue" in glass fibers. However, plastic fibers are quite vulnerable to
damage from
chemicals, such as organic solvents, and require coverings, especially if they
are
abraded to expose the core and increase coupling to the external media.
Unfortunately, clear coverings on individual loops and many other optical
structures
tend to defeat the measurement of external media. Because the coverings are of
high optical index of refraction, they will act as frustrators, so that
contacting
materials will impart little additional change in throughput. Coverings that
do not
contact the fibers closely will also defeat the purpose of the sensor, because
internal reflections will be maintained due to air between the covering and
the
protective layer. The coupling region is preferably covered with a lenticular
layer,
2o although other suitable materials may be used.
The choice of optical fibers as a sensing means imparts qualities of safety
and
freedom from electrical interference, both due to the absence of electrical
conductors within the sensing probe. It also makes possible very small and
flexible
sensing structures. The present invention benefits from the use of loops or
bends in
optical fibers as optical sensors, yet overcomes the disadvantages of prior
art
sensing loops. A particular advantage is the virtually complete modulation of
the
coupled light by the presence of liquids and solids, or by induced curvature,
even
though the device includes a protective coating. This makes the device
relatively
insensitive to the presence of contaminants on its surface. Contaminants
cannot
3ci penetrate through the coating to the fibers, and have minimal effect on
the
measured values.
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As such, various embodiments of the invention described herein use optical
fibers or
other light guides to achieve:
a) Detection of a liquid or solid contacting a sensing element with one bend
that
includes a clear protective layer;
b) Discrimination of the type of liquid contacting the element;
c) Measurement of liquid height with multiple elements or multiple bends;
d) Measurement of curvature at a single bend;
e) Discrimination of single from multiple shapes when multiple bends are
applied;
Accordingly, one embodiment of the present invention is to provide an optical
1o sensing device comprising a pair of optical fibers where the fibers are
positioned
side by side, and covered, as a unit, by a layer of optically transparent
material
having a convex arcuate outer surface.
Another important aspect of the present invention is the exploitation of the
shapes of
paired loops or bends to impart an optimal shape to a clear protective coating
that
couples the loops or bends optically. The coating has a shape determined by
the
loops or bends and the flow characteristics of the coating material during its
cure
cycle.
Another important aspect of the present invention is the exploitation of the
shapes of
fibers laid side by side to impart an optimal shape to a clear protective
coating that
2o couples the fibers optically when they are bent. The coating has a shape
determined
by the fibers and the flow characteristics of the coating material.
Further aspects of the present invention include providing a sensor means
that:
a) can be formed into small individual point sensors or a thin, quasi-
spatially-
continuous array;
b) does not expose the fibers directly to the media to be measured;
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c) is capable of discriminating water from hydrocarbons;
d) is capable of detecting and measuring extent of contact with solids;
e) can be used to measure curvature and classify multiple curvatures to
classify
imposed shape.
f) if desired, can have an optical output of zero when not curved. -
g) can be manufactured and instrumented at low cost.
Accordingly, it is another aspect of the present invention to provide an
optical
sensing device adaptable to detect or sense the presence, location and
identity of
external media.
1o Accordingly, it is another aspect of the present invention to provide a
means of
forming a single point sensor or an array of these sensors from fibers that
have
been looped or bent and covered with a layer or layers of durable material,
and yet
provide maximum modulation (90% or more) when exposed to contact by liquids
and
solids. High modulation is desirable in achieving a liquid sensor that is able
to be
used to discriminate between different substances, such as a liquid and a gas,
or
between different liquids, especially in the presence of contaminating
materials.
Accordingly, it is another aspect of the present invention to form sensors
between
fibers of a fiber optic ribbon cable, at desired lateral and axial locations
along the
cable, so that pressure or imposed shape at the sensor locations will generate
a
2c~ signal due to curvature of the cable, associated with the location of the
sensor.
Accordingly, it is a further aspect of the present invention to provide a
sensing strip
with one or more fibers or other lightguides, so that impressed shapes will
generate
signal values from the sensing strip indicative of the class of shape
impressed,
based on combinations of curvatures contained in the shape class.
It is still a further aspect to accomplish any of the above without use of
special pre-
formed optical shapes such as prisms or grooves, but rather to rely on the
natural
shapes of the loops or bends, covered with materials that do not require
special
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forming processes, yet have a shape that produces the desired optical
response.
This also eliminates the need to connect fibers to optical elements such as
lenses or
prisms, thereby simplifying the construction process and increasing the
reliability of
the instrument.
It is still a further aspect of the present invention to be able to construct
a sensor
array without requiring special alignment fixtures or molds to hold the fibers
in place
during and after construction.
It is still a further aspect of the invention to form flat sensor strips, that
can be
applied to flat or gently curved surfaces and used to sense or classify shapes
when
1o impressed upon the surface, or strips that can be curved at desired
locations to
activate a contact sensing capability at said locations.
It is still another aspect of the present invention to provide an inexpensive
optical
sensor device capable for use as a multi-use sensor, such as a single sensor
construction that can be used to sense liquid level, pressure, and shape.
According to one embodiment of the present invention, there is provided an
optical
sensing device comprising a first optical lightguide; a second optical
lightguide with
a portion of its length parallel to and in close proximity to the first
lightguide to form
a coupling region; the first and second lightguides being covered within the
coupling
region; and wherein, light is coupled from the first lightguide to the second
2ci lightguide, when the lightguides are curved out of their plane within the
coupling
region. Desirably, the above cover for the coupling region is formed by a lens
layer
of optically transmissive material having a convex, arcuate outer surface.
In another aspect according to the above, the lightguides are mounted in a
surface
to be deformed by imposed pressures or shapes for purposes of determining
classes and growth of impacted shapes.
According to a further embodiment, the first and second lightguides are
modified for
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enhanced coupling, by abrasion, chemical treatment, heat forming, or notching,
to
lose and collect light in adjacent surface areas facing away from the plane of
the
lightguides in the coupling regions. In this embodiment, coupling may be made
to
occur for both straight and curved lightguides.
According to a further embodiment, used when shape, rather than contact with
external media, is to be measured, coupling may be further enhanced by
addition of
a reflective layer surmounting the lens layer.
A further embodiment includes means for injecting light into the first
lightguide, and
means for detecting the intensity of light coupled into the second lightguide.
Further,
1o according to the above including a means for injecting light into the first
lightguide,
means for detecting the intensity of light coupled into the second lightguide,
and
means for detecting the intensity of light carried through the first
lightguide.
According to another alternative embodiment, the lens layer is formed on only
the
side of the plane of the lightguides containing the loss and collection areas,
thereby
enabling coupling only for curvatures of the lightguides which impose convex
curvature on the lens layer.
Preferably, according any of the above embodiments, the transparent material
comprises a synthetic resin, a heat dissolvable material or a chemically
removable
material.
2a According to another aspect of the present invention, the first and second
lightguides are formed into curves out of the plane of the lightguides, within
the
coupling region.
In another alternative embodiment, there is provided a pressure or shape
measuring
and classifying sensor as described above, wherein the first and second
lightguides
are mounted on a surface to be deformed by imposed pressures or shapes.
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According to another aspect of the present invention there is provided a
pressure or
shape measuring and classifying sensor wherein the lightguide diameter and
coupling enhancement means are chosen to produce coupled light intensity that
is
maximal for only a single inflected shape and is attenuated when more than a
single
inflected shape is imposed. Desirably, the lightguide diameter and coupling
enhancement means are chosen to produce coupled light intensity that is
maximal
for shapes with large curvatures and minimal for shapes with minimal
curvature.
According to another embodiment of the above pressure or shape measuring and
classifying sensor, the lightguide diameter and coupling enhancement means are
1o chosen to produce coupled light intensity that decreases for noninflected
shapes
and increases for inflected shapes, or to produce coupled light intensity that
is
minimal for inflected shapes and maximal for noninflected shapes.
According to various alternative embodiments described above, there is
provided a
pressure or shape classifying sensor comprising a first or second lightguide
wherein
the intensity of light that has passed through the lightguide is measured to
classify
the shape imposed on said lightguide according to the number of inflected
curves,
polarity of curvature, and magnitude of curvature.
In a further alternative embodiment according to the present invention there
is
provided a pressure or shape measuring and classifying sensor comprising a
first
2n plurality of sensors (as described in an above alternative embodiment),
exposed to
a distribution of curvature within an extent; and a second plurality of
sensors (as
described in an above alternative embodiment), exposed to a distribution of
curvature within the extent; wherein the measurements of a pressure or shape
distribution by the sensors are analyzed singly and in combination to classify
the
distribution of curvature within the extent according to absolute value,
polarity,
number of inflections, number of peaks, spatial frequency content, and
location
within the extent, and to measure the time progress of the classifications.
Desirably,
the above may be used for determining classes and growth of impacted shapes in
vehicles for purposes of safety system deployment. Preferably, the above
sensor
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may be used for determining occupant position and weight in vehicles for
purposes
of protection activation.
According to another alternative embodiment of the present invention, there is
provided a pressure or shape sensing array comprising sensors with coupling
regions as described in any of the above embodiments, distributed over an area
within which pressure or shape is to be measured at locations, wherein the
sensor
coupling regions are located to respond uniquely to pressure or shape at said
locations and wherein the overall pressure or shape is inferred from the
individual
sensor measurements. Preferably, the above sensor array comprises electrical
1o conductors instead of lightguides, the coupling regions comprise electric
coupling
regions wherein coupling is modulated by bending, and the bending is
determined
by measuring electric current or voltage resulting from the coupling.
Desirably, the
above sensors are formed from adjacent fiber pairs of a fiber optic ribbon
cable,
wherein each coupling region occupies a known location along the axial extent
of
the cable.
According to another alternative embodiment of the present invention, the
sensor is
preferably located between first and second mechanical layers, said mechanical
layers containing structures capable of bending the sensors when pressure is
applied or shape is imposed through bending.
2c~ According to any of the above alternative embodiments, there is provided a
media
contact or deformation measurement sensor wherein the combined loss and
coupling properties of coupling regions modulate the light flux passing from
one
fiber to another across the coupling regions, wherein the properties of the
coupling
regions may be chosen to enhance modulation by contact with liquid, or by
imposed
pressure, bending, or shape.
According to an alternative embodiment of the present invention, there is
provided a
liquid or solid contact measurement sensor wherein the coupling regions are
preformed into curves that couple light maximally when surrounded by a medium
of
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low index of refraction and which couple light minimally when surrounded by a
medium of hagh index of refraction. Desirably, the above sensor is one in
which a
flexible surrounding material containing air at atmospheric pressure within is
deflected by pressure from a liquid or solid medium without, to touch the
curved
coupling regions and produce changes in the measured intensity of light
indicative
of contact.
According to another embodiment, there is provided a liquid or solid contact
measurement sensor comprising a sensor with coupling regions preformed into
curves along its extent, each curve of which couples light maximally when
1c~ surrounded by a medium of low index of refraction and which couples light
minimally
when surrounded by a medium of high index of refraction.
According to any of the above alternative embodiments, the sensors may include
a
planar support member having an edge, and where the coupling regions may
extend
over the edge or may be spaced apart along and extend over the edge.
In yet a further embodiment a liquid or solid contact measurement device as
above,
the coupling region is preformed into a curve with its apex exposed at the end
of a
tube covering the device. Desirably, the above liquid contact measurement
devices
measure the intensity of coupled light when the device is immersed in liquid
indicating the index of refraction of the liquid or level and composition of
layered
2ci liquids.
According to another embodiment, there is provided a liquid or solid contact
measurement sensor as described above including an array with spaced sensors,
and motive means for changing the liquid or solid level with respect to the
sensor
array by a known displacement up to one intersensor spacing, the array
measurement and said displacement being used to determine liquid or solid
height
or composition along a continuum.
In an alternative embodiment, there is provided a method of sensing a pressure
or
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shape comprising the steps of providing a first optical lightguide, providing
a second
optical lightguide with a portion of its length parallel to and in close
proximity to the
first lightguide within a coupling region, covering the first and second
lightguides
within the coupling region, as a unit, by a lens layer of optically
transmissive
material having a convex, arcuate outer surface, transmitting light from a
light
source through the first optical lightguide, measuring the intensity of light
coupled to
the second lightguide through the lens layer, by measuring its intensity at
the end of
the second lightguide toward which said coupled light is directed, as a means
of
measuring curvatures within the coupling region.
1o In another alternative embodiment there is provided a method of sensing
liquid or
solid contact comprising the steps of providing a first optical lightguide,
providing a
second optical lightguide with a portion of its length parallel to and in
close proximity
to the first lightguide within a coupling region, covering the first and
second
lightguides within the coupling region, as a unit, by a lens layer of
optically
transmissive material having a convex, arcuate outer surface, forming the
coupling
region into at least a single curve, transmitting light from a light source
through the
first optical lightguide, measuring the intensity of light coupled to the
second
lightguide through the lens layer, by measuring its intensity at the end of
the second
lightguide toward which the coupled light is directed, as a means of measuring
the
2o contact of liquid or solid and the index of refraction of the liquid or
solid.
In a further alternative embodiment, there is provided an optical sensing
device
comprising an optical lightguide, an actuation operable device associated with
the
optical lightguide, wherein the optical lightguide when deformed forms a
coupling
region adapted to transmit light along its length when the lightguide is
curved out of
its plane to the actuation device. Desirably, the above device includes means
for
injecting light into the lightguide, and means for detecting the intensity of
light
coupled into the lightguide. Further, the above device is preferably provided
with a
cover for the coupling region formed by a lens layer of optically transmissive
material having a convex, arcuate outer surface.
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According to another aspect of the present invention, the above lightguide may
be
formed into curves out of the plane of the lightguide, within the coupling
region.
Desirably, the above lightguide may be mounted on a surface to be deformed by
imposed pressures or shapes.
According to an alterative embodiment according to the above embodiment, the
device is provided for determining classes and growth of impacted shapes in
vehicles for purposes of actuating a safety system actuation device.
Desirably, the
device further provides for determining occupant position and weight in
vehicles for
purposes of safety system deployment
1« According to another alternative embodiment, the device may be used for
determining classes and growth of impacted shapes along gaskets and seals.
Preferably, the above lightguide is mounted in a surface to be deformed by
imposed
pressures or shapes for purposes of determining classes and growth of impacted
shapes.
When used to measure pressure, bending, and shape, when it is not desired to
have interactions with external media such as liquid contact, the coupling
regions of
the device preferably include a reflective layer surmounting the lenticular
region, to
increase the light coupled across the coupling zone and extend the range of
curvatures and pressures measurable with the device.
2n According to another preferred embodiment, the device may be used to sense
shape and liquid contact using coupling regions formed with lightguides of
zero
curvature, by enhancing the loss of light from lightguides in the coupling
regions
through abrasion, heat forming, notching, or chemical treatment. For shape and
bend sensing alone, coupling is optimized by such loss enhancement, combined
with the addition of the above reflective layer.
According to another preferred embodiment, the coupling regions in the device
may
each be made responsive to a particular wavelength or band of wavelengths of
light,
CA 02307468 2000-OS-03
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through adding wavelength filtering media to the lenticular medium or
reflective
layer of each coupling region.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, with reference to the drawings.
FIGURE 1 is a side view of an optical fiber curved sufficiently to emit light,
emitting
light.
FIGURE 2 is an edge view of the same fiber in Figure 1.
FIGURE 3 is a side view of the fiber of Figure 1, receiving light.
FIGURE 4 is an edge view of the fiber of figure 3, receiving light.
1o FIGURE 5 is a graph plotting the optical throughput of a fiber as in
figures 1 - 4,
when bent at various curvatures.
FIGURE 6 is a perspective view of two fibers coupled by a lenticular layer
along a
coupling region, including options for enhanced coupling comprising a
reflective
layer and enhanced loss treatment.
FIGURE 7 is a plan view of the fibers of Figure 6, straightened and including
a light
source and receiver, but without the options for enhanced coupling.
FIGURE 8 is a cross section through the two fibers on the line A-A of Figure
7.
FIGURE 9 is an edge view of the fibers as in Figure 7, bent within the
coupling
region.
CA 02307468 2000-OS-03
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FIGURE 10 is a perspective transparent view of curved fibers as in figure 9,
including a lenticular layer along a coupling region.
FIGURE 11 is an edge view of the fibers of figure 10, showing light emitted
from one
fiber, reflecting internally within the lenticular layer, and entering the
second fiber.
FIGURE 12 is a cross section on the line B-B of Figure 10, showing the
coupling of
light from fiber to fiber within the lenticular layer.
FIGURE 13 is a graph of the optical intensity throughput for light injected
into one
fiber of a coupled pair as in figure 10, for varying amounts of curvature of
the
structure.
o FIGURE 14 is a perspective view of two fibers coupled by a lenticular layer,
treated
to have enhanced coupling areas along their upper surfaces, to enhance their
ability
to couple light from one fiber to another at lower curvatures than untreated
fibers.
FIGURE 15 is a cross section of the line C-C of Figure 14.
Figure 15a is a cross section as in Figure 15, but with the addition of a
reflective
layer surmounting the lenticular layer.
FIGURE 16 is a perspective view of a coupled fiber structure as in Figure 15,
but
with multiple enhanced coupling areas applied along the upper surface, for
piecewise continuous coupling between the two fibers.
FIGURE 17 is a schematic view representing the fibers as in Figure 16, with a
20 longer coupling area indicated by the region containing overlapped lines.
FIGURE 18 is a schematic view representing the same two fibers of figure 17,
bent
in a single inflected shape within the coupling area.
CA 02307468 2000-OS-03
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FIGURE 19 is a schematic view representing the same two fibers of figure 17,
but
with two inflected shapes applied within the coupling area.
FIGURE 20 is a graph showing total throughput vs, number of separate curves,
for a
mathematical model of a coupled fiber structure as in Figure 17, for different
attenuations at each curve, and a normalized throughput of 1.0 for each curve,
before attenuation is applied to each coupled throughput.
FIGURE 21 is a schematic view of a coupled fiber sensor as in Figure 17, with
multiple sinuations that can be used to sense the level of a liquid or amount
of
contact with a solid surtace. The fibers include a turnaround loop so that
light source
1 o and detector may be co-located.
FIGURE 22 is a schematic view of a single fiber sensor with a light source at
one
end and a light intensity detector at the other end.
FIGURE 23 is a schematic view of a fiber sensor with two parallel runs of
fiber
coupled by a loop, so that source and detector are co-located and the net
throughput is a product of the throughput of individual purposely imposed
enhanced
coupling areas along the fibers and curvatures imposed on the fibers by an
external
force, said enhanced coupling areas optionally having different
characteristics on
each fiber.
FIGURE 24 is a schematic view of a coupled fiber structure with one fiber
extended,
2o so that throughputs may be measured for light that traverses one fiber from
beginning to end, and for light that traverses in lenticularly coupled fashion
from one
source on one fiber to a detector on the other fiber.
Figure 25 is a schematic view of a coupled fiber structure of Figure 24, with
loops '
incorporated so that all sources and detectors may be co-located and more than
one
fiber run traverses the sensor area, each run being coupled by a loop to the
next
run, so that detected signals are the product of multiple runs.
CA 02307468 2000-OS-03
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FIGURE 26 is a perspective view of a lenticularly coupled sensor in the end of
tubing.
FIGURE 27 is an edge view of the sensor of Figure 26, with the transmitting
fiber on
the left.
FIGURE 28 is an edge view of the sensor of Figure 27, with the transmitting
fiber on
the right.
FIGURE 29 is a perspective view of two elements of an array of lenticularly
coupled
sensors, built on the edge of a thin band of steel.
FIGURE 30 is a simplified view of a complete array of four paired loops or
bends
~ci attached to an interface box.
FIGURE 31 is a simplified view of an alternative embodiment of the present
invention including a complete array of four paired loops attached to an
interface
box, arranged in a standpipe to measure liquid height.
FIGURE 32 is a pressure sensor array formed from fiber optic ribbon cable,
with
coupling zones formed at discrete locations between fiber pairs by forming a
clear
lenticular structure at each location.
FIGURE 33 illustrates a coupled fiber arrangement with mirrored ends.
FIGURE 34 illustrates a mirror ended arrangement having multiple zones.
FIGURE 35 illustrates a mirror ended arrangement having multiple zones, the
zones
20~ angled.
Having thus generally described the invention, reference will now be made to
the
CA 02307468 2000-OS-03
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accompanying drawings illustrating preferred embodiments.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As illustrated in Figures 1 and 2, a fiber 10 curved sufficiently, will lose
light along its
periphery because some of the higher modes are unable to reflect internally
within
the fiber core. For simplicity, a thin cladding layer of low index of
refraction, typically
surrounding the core of all step index fibers, is not shown in the figures
unless
otherwise indicated. The cladding layer 24 is used to maintain internal
reflection
within a straight fiber even if it comes into contact with solids or liquids.
If there is no
such contact, air will serve as a low index of refraction material to maintain
internal
~ o reflections. Whether or not there is a cladding layer, a fiber curved
below its
minimum bend radius will begin to lose light. Example rays of light YY are
shown
leaving the fiber 10 where it is curved.
Although the term "fiber" for "fiber optic" is used throughout the
description, it is
meant to apply generically to lightguides of various types, including clad or
unclad
bars of clear plastic or glass, of round, rectangular, or other cross section,
capable
of guiding light within the bar due to internal reflection.
Figure 2 shows the fiber 10 of Figure 1 from the edge. Example rays of light
YY are
seen to be emitted not only within the plane of the loop, but within a cone of
angles
bisected by the plane of the loop.
2c~ As shown in Figure 3, a fiber 10 bent sufficiently to lose light is also
capable of
receiving light within the same range of angles that it can be emitted.
Example rays
YY are shown entering the fiber 10 where it is curved.
Figure 4 shows the fiber 10 of Figure 3 from the edge. Example rays of light
YY are
CA 02307468 2000-OS-03
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seen to be received not only within the plane of the loop, but within a cone
of angles
bisected by the plane of the loop. After entering the receiving fiber, the
light will
continue to propagate down the fiber 10 within the cone of angles determined
by the
index of refraction of the core and that of its cladding 24, or other
surrounding
medium.
Figure 5 is a curve illustrating the loss of light throughput for a 0.25 mm
diameter
multimode step index plastic optical fiber 10 bent in a 180 degree circular
curve (a
"C" shape) at various radii in air. Throughout this description, throughput is
defined
as intensity of light collected at the output of an optical system under
conditions of
o constant light input. In this figure, unattenuated throughput is represented
by a value
of 1Ø The fiber 10 begins losing light at a radius of approximately 5 mm,
and
continues to lose more and more light as the radius decreases. Larger fibers
begin
to lose light at larger radii. For instance, a 0.5 mm fiber will begin to lose
light at a
mm radius, a 1.0 mm fiber at 20 mm, etc. A similar graph could be generated
showing the receptivity of a fiber to external light along a curved section,
with
receptivity to a wider range of angles corresponding to smaller radii of
curvature.
Figure 6 illustrates a dual fiber 12, 14 sensor structure. The fibers are
parallel and in
close proximity within a "sensing zone" or "coupling region" 20 that is
covered by a
lenticular layer 22 of clear material. The lenticular layer 22 may be applied
to the
2c~ full length of the overlapped fibers 12 and 14, or to a subset of the
length. For
convenience or to provide mechanical protection, the same material may coat
the
non-overlapped fibers. Figure 6 shows the core material 8 of the fibers,
having a
high index of refraction, and the cladding layer 24, having a lower index of
refraction. It is also possible to omit the cladding layer if the cores have
little contact
with materials of high index of refraction, such as by using acrylic rods
extending in
air. Also shown are loss treatments 113 which are optionally used to increase
the
egress and ingress of light through the core-cladding interface, and a
reflective layer
116 which may be used to further enhance coupling and increase the range of
operation of the sensor when coupling to external media is not required. These
3ti optional coupling enhancements are discussed further in association with
Figures
CA 02307468 2000-OS-03
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15, 32 and 33.
Figure 7 shows the fibers and coupling region of Figure 6 in plan view, with
the
fibers straightened and with a light source 16 and light receiver 18, coupled
to
lightguides 12 and 14. For simplicity, the cladding layer 24 and the optional
structures 113 and 116 of Figure 6 are not shown.
Figure 8 is a cross section through the overlapped portion of the sensor
structure
within the coupling zone 20. By way of example, in this figure, the core 8 and
cladding 24 on the fibers 12, 14 is shown. The lenticular layer 22 is shown as
an
oval shape surrounding the fibers. The following conditions apply to the
lenticular
1c) layer:
a) It can be of any shape capable of reflecting light from one fiber to the
other
along tines defined by the emission and receiving characteristics of fibers
curved below their minimum radii of curvature or with cladding modified to
enhance egress and ingress of light. Typical cross section shapes are
convex as shown or flat. Even concave shapes will serve.
b) It can be on one side of the fibers or both. If it is on one side, the
sensor
will only function when it is curved convexly on that side.
c) It can be of any index of refraction higher than that of air. Preferably,
it will
have an index in the 1.5 or higher range, typical of most materials capable of
2o coating fibers. However, the sensor will function when lower index
materials
are used, such as silicones in the 1.4 -1.5 range of index of refraction.
d) It should have sufficient clarity to transmit light the short distance from
one
fiber to the other, but need not be of exceptional clarity. Ordinary epoxies,
urethanes, casein resins and other coatings will function well for the short
path encountered by light traveling from one fiber to the other.
CA 02307468 2000-OS-03
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e) It may be covered by a layer of other material of low index of refraction,
or
by a purely reflective material such as a metal film, for protective purposes
or
for cases where the sensor is to be used primarily as a means of sensing
shape, with minimum coupling desired to external media and maximum
coupling desired from fiber to fiber.
The fibers within a lenticular layer 22 should be in close proximity, or the
lenticular
layer 22 made thicker to enable light to couple at the necessary angles for
propagation when the fibers are bent. In most embodiments, the fibers will be
touching in the overlapped regions, but can be several millimeters apart if
the
lenticular layer 22 is thicker.
Preferred methods for forming a lenticular layer 22 on adjacent parallel
fibers
include:
a) Spreading a synthetic light transmitting resin on the fibers with a spatula
to
fill the grooved space between the fibers. The resin will take on a flat or
crowned cross section due to surface tension effects while curing.
b) Applying a continuous bead of synthetic light transmitting resin on the
fibers through a syringe tip, with size of the bead controlled so that when it
is
curing, it will fill the grooved space between the fibers, taking on a crowned
shape in cross section.
2o c) Applying an excess of synthetic light transmitting resin on the fibers,
and
wiping it off with gloved fingers or flexible spatulas so that when it is
curing, it
will fill the grooved space between the fibers, taking on a crowned shape in
cross section.
d) Any of the above, where the grooved space on both sides is covered with
resin simultaneously, the fibers being suspended in air.
CA 02307468 2000-OS-03
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e) Any of the above, where the fibers are held together with temporary
adhesive while the resin is being applied.
A reflective layer may be added by vacuum or chemical deposition of metal
vapour
on the lenticular region after it is formed, or by adhesion of metal foil or
other
reflective material such as reflective beads, prisms, or colloidal
suspensions. The
lenticular shape of the coupling material is also a preferred shape when used
with a
reflective material. A reflective layer directly on the fibers would prevent
coupling.
The lenticular shape allows space for light to exit one fiber, and then enter
the other
fiber.
o For straight lightguides with intact cladding, as shown in Figure 7, there
is negligible
coupling of light from one fiber to the other in the coupling zone, so there
is no
signal detected by the light receiver. In the present invention, evanescent
coupling
between adjacent fibers, which arises from photons having no finite boundaries
according to the wave theory of light, is not considered to be a significant
contributor
to any of the coupled light.
Figure 9 shows the sensor structure of Figures 6 and 7, now in edge view, but
with
the sensing zone 20, covered by transparent material 22, bent in a 180 degree
curve at a curvature where the untreated fibers are capable of emitting and
receiving light.
2o Figure 10 shows the sensor structure of Figure 9 in more detail, including
the two
curved portions of the fiber in close proximity to each other, and surrounded
by the
lenticular layer 22.
Figure 11 shows the sensor structure of Figure 10 in edge view, including
arrows
indicating the paths followed by example rays leaving the emitting fiber,
reflecting
internally within the lenticular layer 22, and entering the receiving fiber.
Figure 12 shows the sensor structure of Figures 10 and 11 in cross section,
CA 02307468 2000-OS-03
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including arrows indicating the paths followed by example rays leaving the
emitting
fiber, reflecting internally within the lenticular layer 22, and entering the
receiving
fiber. In this figure the cladding layers are shown on the fibers.
Figure 13 is a graph of the coupled throughput of the sensor structure of
Figure 9,
for a 180 degree, or "C" shaped curve, for different radii of the curve. For
radii
above the minimum bend radius of 5 mm, there is very little or zero
throughput,
whereas the throughput rises dramatically as the curvature (curvature is the
inverse
of radius of curvature) increases.
Figures 14 and 15 illustrate a sensor structure including overlapping fibers
o surrounded by a lenticular layer 30, in a sensing zone 32. In this case, the
fibers are
treated to lose light along narrow strips by abrading or other methods
described in
patents by Danisch, US 5,321,257, US 5,633,494, and WIPO 0,702,780 to increase
their ability to modulate throughput in response to bending. These treatments,
shown in Figure 14 as short parallel lines 34 along fiber 26 and similar lines
36
along fiber 28, and on Figure 15 as striped regions in the core-cladding
interface at
the tops of the fibers also serve to couple light into the fiber, so serve as
a means of
"enhanced coupling" between the fibers even when they are straight or bent
without
violating the minimum bend radius. In this alternative embodiment, the
treatment is
applied to enable use of the sensing zone 32 at large radii of curvature. For
2o instance, the structure used to generate the graph of Figure 13 has no
throughput
for radii above approximately 5 mm, but the same configuration with abraded
zones
as in the present figure begins to lose light for radii of 10 cm, and wider or
deeper
"enhanced coupling" zones can be applied to achieve coupling even for straight
fibers. If the enhanced coupling zones are restricted to one side of the
fiber,
coupling will increase for bends that curve the enhanced coupling zones
convexly,
even for large radius bends, but coupling will normally be minimal or zero for
bends
in the other direction until microbending effects begin to take place (e.g. 5
mm
radius for the fibers in this example). An exception to this can be created
with fibers
that have enhanced coupling zones with very high loss or where an optional
3o reflective layer 116 is added above the lenticular layer, as shown in
Figure 6 or
CA 02307468 2000-OS-03
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Figure 15. Then, coupling may be nonzero even for straight fibers, and will
decrease to zero when the enhanced coupling zones are increasingly concave.
Given that loss strips may be applied in various lengths, spacings, and
conformations given in Danisch '257, '494, and '780, including on one side or
two
sides, or circumferentially around the fibers, many throughput vs. curvature
characteristics are possible. An example of bipolar enhanced coupling zones
distributed along the fibers in quasi-continuous fashion is shown in Figure
16. The
distribution is made quasi-continuous to prevent depletion of loss modes as
described in Danisch '257, '494 and '780. It is also desirable to displace the
~o collection zones 40 "downstream" (away from the light source) of the loss
zones 42,
because light loss occurs at angles directed away from the source, and
collection is
optimal for angles directed toward the source. A typical downstream
displacement
for 0.25 mm fibers is 0.5 to 1 mm.
The embodiment shown in Figure 15a is similar to Figure 15, but shows a
reflective
layer surmounting the lenticular layer.
Characteristics of coupled fiber structures with different types of enhanced
coupling
zones include:
a) Monopolar: throughput responds equally to curvatures of either polarity.
This can be achieved with untreated fibers beyond the minimum radius of
2o curvature, or with fibers treated on both sides or circumferentially,
within a
larger range of radii. Monopolar sensors respond to the absolute value of
curvature.
b) Bipolar: throughput increases for one polarity of curvature, decreases or
is
unchanged for the other. This can be achieved with fibers treated heavily on
one side and can be further enhanced by using a reflective layer over the
lenticular layer.
c) Nonuniform or nonlinear: throughput responds differently for different
classes of curvature. For instance, the throughput of coupled fibers treated
CA 02307468 2000-OS-03
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with enhanced coupling zones will respond with gradual changes to large
radius bends, and will respond with increased sensitivity to bends within the
range of radii where microbending effects predominate.
d) Spatially varied: If enhanced coupling zones are applied with varied
spacing and length, coupled fiber structures may be achieved that have
zones of sensitivity and insensitivity along their lengths. Curvatures applied
to the fibers may tend to miss the sensitive zones, or be poorly sampled by
the sensitive zones, or not have any effect or minimal effect in zones that
are
purposely designed to be insensitive or minimally sensitive to curvature.
o All of the light coupled from one fiber to another in a coupled fiber sensor
without
the addition of a reflective layer, as in Figure 9 relies on internal
reflection within the
lenticular layer 22. Without internal reflection, which relies on the presence
of a
medium of low index of refraction compared to that of the lenticular layer 22,
surrounding the lenticular layer 22, coupling will be reduced to a lesser
value or to
zero, depending on the index of the surrounding medium and its extent of
contact
with the curved portion of the fibers. The following are examples of measured
throughput for various media surrounding lenticularly coupled loops with a
radius of
1 mm, referenced to a normalized value of 1.0 for air:
a) Air (index of 1.00): 1Ø
2o b) Water (index of 1.33): 0.08
c) Motor oil (index of 1.43): 0.04
Many other hydrocarbons have indices in the 1.4 to 1.5 range, and produce
results
similar to that of motor oil, and always easily distinguished from those of
water or
air. When solids come in contact with a curved coupled fiber sensor, the
coupled
light is also frustrated, to a degree dictated by the contact surface area.
The surface
area of liquid contact also determines the throughput for a single loop, the
throughput rising to a maximum for total contact.
CA 02307468 2000-OS-03
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Figure 17 shows a coupled fiber structure in schematic form, with the fibers
12, 14
drawn as two parallel lines, overlapping within an oval shape 20 of
exaggerated
width, meant to represent the coupling region formed of transparent material
22.
Figure 18 shows the fibers of Figure 17 with a curvature applied in the shape
of an
inflected curve 50. This may be thought of as the shape of a dent applied to
the side
of an automobile, or curves in a flexible coupled fiber pressure sensor caused
by
pressure from an object such as a finger, or could represent fibers that are
held in
constant curves so that liquid or solid contact may be sensed at the curves.
The
curves are said to be inflected because they include positive and negative
values of
10~ curvature. The two polarities of curvature are illustrated schematically
by upward
convex arcs 53 representing negative curvature and downward convex arcs 55
representing positive curvature. In this example, the two positive curves have
a net
angular change of approximately 90 degrees each, and the negative curve has a
net
angular change of approximately -180 degrees. The algebraic sum of the net
angular curvatures is zero. This is confirmed by the fibers entering and
exiting the
inflected curve in the same horizontal orientation.
Figure 19 shows the fibers of Figure 17 with two inflected curves 52, 54
applied at
different locations along the coupled portion of the fiber.
Figure 20 depicts the calculated throughput of a sensor as shown in Figure 19,
but
2o with the number of inflected curves varying from one to five. It will be
described in
more detail below as the equations for throughput are derived.
Figure 21 depicts a sensor as in Figure 17, but with multiple sinuations 58
preformed in the coupling region, which is indicated by the overlapped fibers
within
the sinuated oval shape representing the lenticular transparent material 22.
It will
be described in more detail below in the context of liquid sensing. It is
presented
here in association with Figure 19, as an example of a coupled fiber sensor
with
multiple sensing curves 58 and a non-sensing turnaround loop 60. In the case
of
Figure 19, the multiple curves result from a temporarily imposed shape. In
Figure 21
CA 02307468 2000-OS-03
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they are permanently pre-formed to enable contact sensing of a liquid.
We now address the issue of throughput for single and multiple curves along
the
fibers. First, we will consider a single fiber 12 like one of the fibers shown
in Figure
17, but with source 16 and detector 18 connected to the two ends. Such a fiber
is
shown in Figure 22 and again in Figure 23. In Figure 23 a loop 60 is
incorporated
so that source and detector may be co-located, and two runs of fiber 13 and 15
coupled only by the loop 60, but exposed to the same imposed curves along
their
lengths, may be treated differently by means of purposely imposed enhanced
loss
zones of different constructions, so that each run contributes in a different
way to
o the net throughput signal when curves or contacts are imposed on runs 13 and
15
simultaneously. The different treatment of the runs 13 and 15 is indicated
schematically by different linestyles for each run. . Within a single fiber
run or runs
coupled only by a loop of the same fiber and with no other coupling means
used, the
net throughput is a product of the losses at each curve. If a fiber has n
curves, each
curve i in the fiber has a throughput Ei resulting from microbending or
purposely
imposed loss zones, and if Es is the net throughput of such a single fiber
(normalized to unity for unattenuated throughput) , then
(Eq. 1 ) Es = ~Ei, where the product ~ is taken from the initial through the
nth
curve i.
2o Thus, if 6 equal curves each of throughput 0.5 are applied, the net
throughput
Es=(Ei)"=0.5x0.5x0.5x0.5x0.5x0.5=0.016.
Three curves of throughput 0.5 result in Es= 0.125, or 8 times more throughput
than
6 curves.
The "6 curve" vs "3 curve" example is relevant to comparing the effects of a
single
dent to those of double dents, where each dent includes a positive and two
negative
curves of equal magnitude, and the coupling is monopolar (equal for any
polarity of
CA 02307468 2000-OS-03
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curvature). At first it might seem useful to have multiple dents produce less
throughput than a single dent, but it must be remembered that in a single
fiber
sensor, reduction in throughput is a signal indicating increasing depth of a
dent, so
that multiple small dents will mimic a single large dent. This is the opposite
effect to
that desired for air bag or other safety system deployment, for which one may
wish
to ignore multiple small dents. However, a single fiber sensor may be useful
in
detecting sharp vs. broad dents. The former will produce more attenuation than
the
latter, due to the larger curvatures implied by sharp vs. broad dents.
By varying the type and placement of loss zones, it is possible to create
single fiber
o sensors that respond differently to different shapes. In the example above,
the
sensor responds with increasing attenuation to higher curvatures or more
dents. If
enhanced coupling zones of minor attenuation are applied to one side of the
fiber,
then a saturated response in throughput to bends of a given polarity can
result. As
shown in Danisch, US 5,633,494, and WIPO 0,702,780, a lightly treated (an
imposed enhanced coupling zone with small attenuation) sensor fiber will
exhibit a
throughput that saturates at a high value for concave bends of the treated
zone
above a characteristic curvature, and which continues to decrease for
increasing
bends in the opposite, convex direction.
If such a sensor is used to detect dents, it will have an accentuated response
to
2o bends in the convex direction, so that it can be used, for instance, to
classify
inflected dents from noninflected (monotonic) dents. This is done by applying
the
sensor so that noninflected dents cause convex curvature of the treated zones,
thereby causing an increase in throughput that saturates, whereas inflected
dents
will cause a large net decrease in throughput due to the imposition of two
concave
curvatures with unsaturated decreasing throughput at the edges of a single
convex
curvature that saturates at a low value of increasing throughput. If the
sensor is
inverted so that noninflected curves cause a decrease in throughput, they will
be
sensed as a non-saturated decrease in throughput. Inflected dents will also
cause a
decrease in throughput, representing the product of one convex curve (large
3o unsaturated decrease) response with two concave curve responses (small
saturated
CA 02307468 2000-OS-03
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increases). Sharp inflected dents will produce larger drops in throughput than
broad
inflected dents, since most broad inflected dents will have two concave edges
that
are below the saturation limit, and will have a net zero product, the net
result of one
small decrease and two small increases.
Others may be made into sensors that have no treatment, in which case they
will
respond with attenuation that increases for sharper bends or more bends,
without
regard to polarity of curvature within the microbending range; or with loss
zones on
both sides, so that response also disregards polarity but is not restricted to
the
microbending range; or with loss zones on one side but such that response is
o bipolar (regards polarity of curvature) over a broad range of curvatures (as
opposed
to the bipolar saturated response described above). Treated fibers with a
bipolar
response may also be used to classify noninflected shapes from inflected
shapes.
Inflected shapes that begin and end with zero curvature have a net curvature
of zero
regardless of the curvatures within the shape, so will be "invisible" to a
bipolar
sensor. In contrast, a bipolar sensor will detect noninflected shapes easily,
as they
have a net positive or negative curvature.
Multiple sensors with different characteristics may be added to a door panel
or the
side, front or any other surface of a vehicle to classify impacts by shape and
to
deploy air bags, air curtains, or other safety devices, depending on the shape
class
2o and the magnitude of the shapes over time. The outputs of the sensors may
be
combined arithmetically in an electronic processor by conventional analog or
digital
means. Combinations include arithmetic addition or subtraction, or logical AND
and
OR operations, based on each sensor triggering a binary logic state indicating
the
class of impact shape detected, and these logic states then being resolved by
AND
and OR combinatorial logic. It is also possible to combine responses within a
single
fiber, by providing multiple runs of the fiber across the region to be sensed,
each
coupled to the next through a turnaround loop. The combination will be a
product of
the individual sensor characteristics, which may be varied by type of
treatment and
by not inverting or inverting the treated portions with respect to convex or
concave
3o shapes.
CA 02307468 2000-OS-03
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A sensor in which there is coupling between the two fibers due to a lenticular
structure has throughput characteristics that are related to the attenuation
effects
exhibited by a single fiber, but modified by coupling effects that tend to
counteract
the attenuations of a single fiber. This suggests combining single fiber
sensors with
lenticularly coupled fiber sensors to better classify shapes. Such a
combination will
be described below, but first we will describe a lenticularly coupled sensor.
For such
a sensor to have a nonzero output, the curves must be of sufficient curvature
to
cause coupling from one fiber to the other, due to microbending or purposely
applied enhanced coupling zones. For each curved region, there will be light
coupled within the curved region. However, a curved region also attenuates
light
passing through either fiber toward other locations along the sensor
structure, both
in the emitting and receiving fiber. This causes the amount of light reaching
the
detector from multiple curved zones to be equal to or less than the amount
from a
single curved zone, for curvatures that each attenuate the light passing by
them by
half or more. For smaller attenuations, the throughput may increase and then
fall off
with increasing numbers of curves, or even continue increasing as more and
more
curves are added.
The attenuation of signals from multiple curves is explained in the following
way:
Each curved zone attenuates light passing through it, from any source, due to
2o microbending or purposely formed enhanced coupling zones or regions. Light
coupled across at any curved zone will encounter transmission fiber losses
from
curves between the light source and the coupling zone or region, and receiving
fiber
losses from curves between the coupling zone or region and the detector. The
number of curves imposing losses will be the same for any coupling zone, since
zones nearer the detector will have fewer receiver fiber losses but more
transmission fiber losses, and zones nearer the source will have fewer
transmission
fiber losses but more receiver fiber losses. For instance, a fiber structure
with 6
equally curved zones along its length, wherein each curve imposes a local drop
in
throughput from 1.0 to 0.5, will have an overall throughput of 0.5 x 0.5 x 0.5
x 0.5 x
30 0.5 x 0.5=.016 for each zone of coupling. We apply only one loss figure at
the
region of coupling because coupling is distributed across the length of the
CA 02307468 2000-OS-03
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curvature. If we consider that each curve would couple a unit amount of light
if no
attenuations occurred, then the total coupled throughput will be the sum of
the
attenuated unit amounts. Each attenuated coupled amount is 1.0 x 0.016 =
0.016, so
the sum, or total throughput is .016 x 6 = 0.096. In contrast, an individual
curve
would have a throughput of 0.5 x 1.0=0.5, or more than 5 times more than the
combined signal from the 6 curves. In this example, three curves would produce
a
throughput signal of 0.125 x 3 = 0.38 compared to the signal of 0.096 for six
curves.
The "6 curve" vs "3 curve" example is relevant to comparing the effects of a
single
dent to those of double dents, where each dent includes a positive and two
negative
curves of equal magnitude, and the coupling is monopolar (equal for any
polarity of
curvature). The double dents produce a signal almost 4 times smaller than a
single
dent of the same magnitude.
If curves of different magnitudes are applied at different locations along a
coupled
fiber structure, then the net effect is of course complicated by the different
amounts
of coupled light, and the differing attenuations, at each curve. However,
increasing
curvature is associated with increasing coupling, so increased coupling is
generally
accompanied by increased attenuation, so the net throughput from multiple
curves
changes only slightly with changes in curvature of the individual curves. This
is to
be contrasted with the very robust increase in throughput for a single curve
with
2a~ increasing curvature.
Even when the curvatures are varied along the coupled fibers, the attenuations
are
the same for light coupled at any of the curves, because both transmitter and
receiver fibers have the same curves.
The net throughput, Ec, for a coupled fiber sensor with n individual curves,
each
with unattenuated coupling Ki for light between the fibers, and attenuation Ai
for light
traveling down a fiber, is given by:
(eq. 2) Ec = (j~Ai)(~Ki), where the product jj and sum ~ are taken over all i
from initial to nth.
CA 02307468 2000-OS-03
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Figure 20 is a graph of Ec vs. n, for various Ai from 0.1 to 0.9. The graph
was
created from a mathematical model in which each coupled throughput is assigned
a
normalized value of 1.0 before attenuations are applied. It can be seen that
for
increasing n, the net throughput either decreases, rises and then decreases,
or
continues to increase, as Ai is varied. For most fibers, the higher Ai values
apply
unless the curvatures are at the low end of values that produce measurable
coupling. Note that in an actual sensor the unattenuated coupled throughputs
would
not have values of 1Ø Instead, they would be small for low curvatures and
large for
high curvatures, so that the absolute magnitudes of the family of plots in the
graph
would be different from that shown, usually opposite to that shown. However,
the
graph is only meant to indicate the variations for each single plot of the
family, as
the number of imposed curves is varied (by "plot" within a family, we mean
what is
usually called a "curve" within a family of curves, but have avoided the
conventional
term to avoid confusion with the spatial curves associated with the shape of
fibers).
The net throughput can be used as a measure of the shape of indentations in
the
side of a vehicle, such as to emphasize safety system deployment for sharp
single
dents vs. sharp double dents. By varying the type and placement of enhanced
coupling zones and Ai, it is possible to create coupled fiber sensors that
respond
differently to different shapes. For instance a sensor with large fibers or
with added
2a~ enhanced coupling zones will respond to broader shapes than a sensor with
very
small fibers and/or no purposely added enhanced coupling zones. As another
example, a sensor with low attenuation per bend might have an output that
increases according to the number of dents, while another with high
attenuation
might have an output that decreases with the number of dents. As a further
example,
a coupled fiber sensor with added enhanced coupling zones could respond to a
broad monotonic curvature, while an untreated sensor would not respond at all
to a
broad monotonic curvature. Multiple sensors with different characteristics may
be
added to a door panel or the side of a vehicle to classify impacts by shape
and to
deploy safety systems depending on the shape class and the magnitude of the
so shapes over time.
CA 02307468 2000-OS-03
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The single fiber sensors of Figure 22 may be combined with lenticularly
coupled
fiber sensors of Figure 23 by extending the transmission fiber 12 of a
lenticularly
coupled sensor with a coupling region 20 formed of lenticular material 22 and
fitting
it with a second detector 18b as in Figure 24. The second detector 18b will
respond
to the net throughput of the transmission fiber 12 alone, the first detector
18a
responding only to light coupled from fiber 12 to fiber 14. The outputs of the
two
sensors may be combined arithmetically or logically as described, so that both
coupled and uncoupled responses may be obtained from the same structure for
use
in a shape classification function.
o The single fiber sensors of Figure 22 or Figure 23 are able to broaden the
classification abilities achievable with a double fiber coupled sensor, since
they
have a different throughput equation when in use. In the latter embodiment, it
is the
same equation whether or not the "single fiber sensor" is a stand-alone device
or is
a portion of a double fiber sensor. While a double fiber coupled sensor has a
throughput equation including product and sum terms (see eq. 2 above), the
equation for a single fiber sensor has only the product term. Shapes including
multiple curves, particularly multiple inflected curves, will result in
different outputs
from the single and double fiber sensors, beyond the obvious distinction that
single
fibers always have a throughput even when straight, which is not always true
of
2o double coupled fibers. An important property of a single fiber sensor with
a
nonlinear response to curvature magnitude is that its output can be made to
decrease as more peaks or inflections are imposed, whereas a double fiber
sensor
can respond to the addition of peaks with little change in output. This means
that it
is possible to use the single and double fiber sensors together to resolve the
number of peaks, and also to gain information about the magnitude of the
applied
curvatures. For example, in the case of a single fiber sensor that saturates
at a
certain positive curvature, its throughput remains constant for curvatures
above a
certain positive value. For a single dent (an inflected curve, or "peak")
containing a
curvature beyond the saturation value, its throughput will decrease. As more
dents
so are applied, its net throughput will continue to decrease. In contrast, the
throughput
of a double fiber coupled sensor can be made to remain approximately the same
as
CA 02307468 2000-OS-03
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more dents are imposed, due to the summing term of equation 2. By comparing
the
outputs of the single and double fiber sensors, one may obtain information
about the
number of dents and their overall magnitude. The single fiber output will
indicate
number of dents, whereas the double fiber output will indicate magnitude of
the
curvature of the "sharpest" (highest spatial frequency) dent.
The ability to classify shapes is a feature of sensors that are long compared
to the
highest spatial wavelengths present in the shape, particularly if it is
possible to
introduce nonlinearities or other local modifications to the magnitude
response of
the sensor. Nonlinearities permit obtaining useful outputs from sets of
curvatures
that would otherwise sum to zero. Other "tuning" factors are given in the
example
introduced in the following paragraph. The ability to tune the response of a
long
sensor to sense shape is an important aspect of the present invention, which
distinguishes it from prior art.
Shape classification may be performed with sensors of any technology that are
able
to combine curvature information along their lengths. Examples include
capacitive
bend sensors and resistive polymer bend sensors, as well as strain gauge bend
sensors. An example of classification of shapes is given below, applicable to
any
sensor technology capable of measuring the integral or product of curvature
along
its length.
2o Definitions used in the example are:
Curvature: C= d6/ds, where 8 is the angular orientation of a space curve and
s is the distance along that curve, regardless of its shape. The space curve
is
taken to be in Cartesian space, with x and y coordinates. Curvature devolves
to d6/dx for shallow shapes, which is similar to the derivative of slope, or
(dy/dx). This approximation is used in deriving beam equations (ref. Crandall
and Dahl, An introduction to the mechanics of solids, McGraw-Hill, NY, p.
362, 1959), but does not hold well for sharp dents.
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Monotonic shape: a shape without inflections of curvature, i.e. the curvature
is all of one sign (positive or negative).
Inflected shape: a shape that contains both positive and negative curvatures.
Note that this definition is for curvature (8,s realm). In the x,y realm a
shape
can have monotonic (all positive or all negative) slope (such as a circular
dent) but will still be inflected in the curvature realm.
Dent: a synonym for inflected shape.
Peak: a synonym for inflected shape.
Integrated curvature: The integral of curvature along s. This is typically
what
o a distributed fiber sensor reports, for all shapes applied along its length
s.
Local integration: It is important to point out that a fiber (or many other
distributed sensors) perform local integration, reporting a single number at
the output. This is what can make them "smart," if we are able to "tune" what
is integrated. Local integration is what produces a zero result for a linear
curvature sensor exposed to an inflected curve that starts and ends with zero
slope. It is important to note that, for instance, the local integral of the
absolute value of curvature will produce a large result, whereas the absolute
value of the integral of curvature will produce a zero result for the
inflected
curve mentioned earlier in this paragraph. Sensors may integrate curvature
2o along their lengths, or form a product of local or incremental curvatures.
A
product, if treated logarithmically, becomes an integral, as the logarithm of
a
product is the sum of the logarithms of the product factors. Also, a product
of
large (close to a normalized value of 1.0) throughputs that decrement by a
small amount behaves approximately as 1-(the sum of the decrements).
Therefore, it is frequently permissible to view a product as an integral.
Either
can be used to perform classification according to the methods given in the
description of the present invention.
CA 02307468 2000-OS-03
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Tuning: Selecting the local sensors along a fiber (or other sensor) so that
the
integral is taken over functions including the following functions or their
combinations (others are possible as well):
a. absolute value of curvature.
b. positive curvature only.
c. negative curvature only.
d. curvature that saturates at a chosen positive magnitude.
e. curvature that saturates at a chosen negative magnitude.
f. curvature selected through a spatial comb filter.
10~ g. responses that vary along s.
In the present example, a table containing important classes for
discrimination of
accident events is provided. It shows discrimination is possible for most of
these by
using two sensors in combination. The sensors are of two types, called "1" and
"2"
with characteristics as described in the table. A third sensor described below
is
sufficient to discriminate a one remaining "problem" case. The third sensor is
similar
to sensors 1 and 2 but employs a specific saturation point for determining a
particular class. The characteristics of sensors 1, 2, and 3 are included in
the
description of various single and coupled fiber sensors given earlier in the
description of the present invention.
20 (Key to the table: si = sharp, inflected; sit = two si dents; bi = broad
inflected; bm =
broad monotonic, 1 xx = output of sensor 1 for xx dent; 2xx = output of sensor
2 for
xx dent; xx = bi, bm, si, or bi).
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Class Sen dent inflectionsno. output can aliasingresole
of
dent sor width of of (pos pos alias is es as
no. curvaturede is larger with resolved
(C) nts than pos) (NA=no by:
t
aliased
si 1 sharp inflected1 pos 1 bi 2 si
sit 1 sharp inflected2 pos pos NA sit
bi 1 broad inflected1 pos 1 si 2 bi
bm 1 broad monotonic1 neg NA bm
si 2 sharp inflected1 pos NA si
sit 2 sharp inflected2 pos pos NA sit
bi 2 broad inflected1 small/zerono dent1 any bi
pos
o bm 2 broad monotonic1 pos 2si 1 bm bm
The logic indicated in the table will resolve all the shapes in a static or
dynamic case
except for the sit case, which relies for detection on the magnitude of a
positive
output relative to another positive output. During the event, a small sit
output can
look like an sit output from a single dent that is very large, so additional
classification means are required.
The si2/si1 problem can be resolved by using a third sensor that saturates
locally at
a critical level of positive curvature and tends to ignore negative curvature.
For this
sensor, deepening sit or sit shapes will saturate at the same depth, causing
the
output to stop increasing at the same time. At (or after) that point in time,
the
2o magnitude of output from a NON-saturating sensor like no. 2 above can be
used to
infer whether it is an sit or sit event. The sit event will always have a
larger
magnitude at sensor 2 when sensor 3 saturates, because it is like two sit
outputs
CA 02307468 2000-OS-03
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added.
Another means of resolving the si2/si1 problem is to use a coupled lenticular
sensor.
Such a sensor can be made to have a very small output for an sit event, and a
very
large output for an sit event, thereby resolving the problem with great
simplicity.
This completes our presentation of the present example.
Figure 25 illustrates a coupled fiber sensor structure that, as in Figure 24,
includes a
detector 18a of light coupled from fiber 12 to fiber 14 and a detector 18b of
light
attenuated within the fiber 12 connected directly to the light source. The
structure of
Figure 25 further includes multiple bends or loops 60 so that the fibers may
traverse
the sensing region multiple times, multiple traverses being exposed to the
same
shapes, and so that the source and detectors may be co-located. With such a
system, it is possible to use different enhanced coupling treatments on each
traverse, so that the net signals are influenced by a combination of
treatments. This
amounts to a form of optical computer, wherein the optical signals are
combined to
infer shape information. The coupling region 20 is shown schematically as an
oval
shape following the overlapping fibers, representing a lenticular material 22.
Alternatively, the coupling structure 20 may be discontinued at the bends or
loops
60 to reduce coupling due to the bends or loops 60.
Figure 21 shows a sinuated lenticularly coupled fiber sensor designed to
provide a
2o signal that decreases as it becomes covered by liquid. It may also be used
to
indicate the extent of contact with a solid surface or surfaces. The
throughput of the
sensor of Figure 21 may be calculated according to Equation 2. If the
sinuations are
equal and of moderate curvature, then the sensor in air will tend to have a
net
output that varies little with the number of sinuations, as indicated in the
curve for
Ai= 0.7 in Figure 20. As each sinuation becomes covered by liquid or contacts
a
solid, its coupling is decreased to near zero, so the sum term of Equation 2
is
decremented by a single Ki as each sinuation is contacted. This results in a
linear
decrease in Ec as liquid or solid contact increases in extent, falling to near-
zero
CA 02307468 2000-OS-03
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throughput for total contact with all the sinuations. This is to be contrasted
with a
single fiber version of the sensor, with source and detector on the same
single fiber.
The throughput of such a sensor is determined by the internal reflection
conditions
at each curve. From experiments with individual curves, we know that the
maximum
attenuation that may be achieved at a single curve that has a covering of
clear
material to protect it is 33%. Thus, a single fiber sensor with successively
immersed
curves would be expected to have a throughput that varies in steps, the net
throughput having values like 1.0, .67, 0.45, 0.30, 0.20, 0.14, etc. if the
throughput
for no contact is normalized to 1Ø This would be a useful sensor, except
that it is
very difficult in practice to achieve a 33% attenuation consistently. The
attenuation
value is highly dependent on the integrity of contact with the covering layer
and the
thickness and microscopic shape of the layer. This makes it difficult to form
lookup
tables in software to deal not only with the power law of the stepped
attenuation
function, but also with variability in each attenuation, which typically leads
to
attenuation values for single loops that vary from 10% to 33%. In contrast,
the
lenticularly coupled structure has a throughput that changes in equal steps
down to
near zero throughput, with each step dropping by 1/n where n is the number of
sinuations. This is because frustration is virtually complete at each curve
and the
throughput is responding to the summation term of Equation 2. This evenly
stepped
2o behavior is little affected by small changes in the thickness or shape of
the lenticular
structure, or by contamination on its surface. Also, the small remaining
throughput
after total immersion can be measured to classify the medium contacting the
sensor,
according to its index of refraction. Typically, water with an index of 1.33
will
produce approximately twice the residual throughput as hydrocarbons, with
indices
typically in the 1.4 to 1.5 range.
The lenticularly coupled sensor structure is also useful for forming arrays
where
each member of the array is a lenticularly coupled sensor with either a single
curve
to detect contact at a point, or multiple curves to detect progress of a
contact front
along the curves of the member until a near-zero throughput is achieved and
the
so next member begins responding to contact. It may be modified, for curves
too
gradual to have significant coupling due to microbending, by emphasizing loss
and
CA 02307468 2000-OS-03
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collection by purposely forming "loss" zones at the curved portions. An array
of
single point contact sensors formed from lenticularly coupled sensors each
with a
single curve and a single light detector, will produce very large changes at
each
detector, typically 90%, as the member associated with the detector comes into
full
contact with liquid or solid. If n sinuations replace the single sinuation of
a point
sensor, each detector will see changes that are approximately 1/n for contact
with
each sinuation. Thus it is possible to form arrays with members that exhibit
either
binary or quasi-continuous changes in throughput, each member having near-zero
throughput for total immersion, with a small residual value indicating the
type of
o medium present according to its index of refraction.
Figures 26, 27 and 28 show two lenticularly coupled fibers 60, 62 from three
different views. The curves in the fibers are of short radius, as the fibers
are
mounted in the end of tubing 72. The curves, or loops, 64 and 66, are adjacent
and
covered with a thin layer of optically transparent material 70, i.e., a clear
epoxy.
Both fibers are shown cut off short on one side of the loop, although that end
may
also be left uncut without consequence. The other, longer side is directed
toward a
light source or detector. As illustrated in Figure 26, a ray that is not
within the plane
of its loops is shown propagating upward in a first loop, where it exits the
first loop
near the apex. Although not explicitly shown in Figure 26, the ray exits at an
angle
2o directed toward the second loop or bend.
As shown in Figure 26, the result of this transfer is shown by the downwardly
directed arrows in the second fiber. Figures 27 and 28 indicate the out-of-
plane
egress of such rays near the apex of the first loop or bend of Figure 26, and
their re-
entry into the second loop or bend, which involves an intermediate internal
reflection
from the optically transparent covering. Vertical arrows near the bottom of
Figures
27 and 28 indicate the general overall direction of light within each loop,
not specific
mode angles. Not all of the light exits the loop or bend, but portions
traveling around
and past the loop or bend are, for simplicity, not shown in the figures.
In a preferred embodiment for forming individual point sensors for a liquid
sensing
CA 02307468 2000-OS-03
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array, loop or bend radii approximately the diameter of the fiber are obtained
by
wrapping 0.25 mm diameter fibers tightly around the edge of 0.25 or 0.125 mm
metal substrate. Other materials for use as substrates include other rigid
elements
such as polyester or glass suitable for use in the medium to be tested. For
other
sensors, such as array elements with multiple sinuations, loops or bends with
larger
diameters may be desirable, for instance to achieve an attenuation to produce
a
desired result from Equation 2. For other sensors such as a side impact shape
sensor, the fibers may be straight initially.
Figure 29 illustrates two elements of an array of paired loops or bends 78,
built on
the edge of a band of spring steel 80. In a typical array, the spring steel is
0.125 mm
thick and 12.5 mm wide, and the fibers are 0.25 mm in diameter. As shown, the
left-
most loop or bend of each pair carries light along the back side of the steel
until it
crosses over to the second loop or bend at the edge of the substrate. The
light then
travels along the second fiber along the front of the steel, toward a
photodetector.
The first loop or bend passes over the part of the second loop or bend at the
back of
the steel. During construction, the loops or bends are pulled tight so that
the fibers
touch the metal virtually everywhere along their lengths and are snug against
each
other and against the steel. If the steel band is narrow as shown, the natural
curves
of the fibers prevent orienting the long axes of the loops or bends
perpendicular to
2o the long axis of the steel, but this does not affect performance. The
important factor
is to achieve snug contact between fibers and to the metal. This occurs
naturally,
aided by the crossover of fibers and the tendency of the leads to both be
placed in
compression when the loops or bends are pulled tight. The loops or bends on
the
steel are covered in clear epoxy or a similar clear film 81, and in fact the
entire
assembly is normally covered in epoxy. Only the loop or bend apexes need
remain
optically clear. The rest of the assembly can be covered with opaque
materials.
Figure 30 illustrates, in a simplified form, an array of four paired loops, as
in Figure
29, attached to an interface box 82.
While they are curing, but still flowable, epoxy or similar clear liquids
naturally form
CA 02307468 2000-OS-03
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the correct shape for transfer of light from one loop to the other. The
requisite shape
is lenticular, in that it follows the curve of the loops in one dimension, and
is nearly
flat or an outwardly convex dome shape between the loops. This shape is ideal
for
the three dimensional path taken by light transferring from one loop to the
other.
Light exits the first loop along its length, and is reflected by a curved
length of the
lenticular surface, with geometry well matched to the curved length of the
second
loop. Thus, light that exits the first loop at multiple points is very likely
to enter the
second loop in a geometrically symmetrical fashion. This result is evident in
the
high throughput of these sensors when exposed to air.
~o Natural liquid forces such as capillary action cause uncured epoxy to flow
in
between the loops and to form a thin covering near the apexes. If optical
throughput
is observed during curing of the epoxy, it will be seen to improve during the
initial
part of the cure, when the epoxy is still capable of flowing. This is in
contrast to
coating two adjacent fibers cut square in the same plane. In that case, there
is no
transfer of light from one to the other, as the geometry deteriorates as the
epoxy
gets thinner on the cut faces of the fibers. For the cut fibers, there is
simply not
enough material on top of the cut faces for reflections to occur from one
fiber to the
other. The only cure would be to add a separately formed lens or reflective
structure.
2o The clear covering material is curved in one dimension, following the
curved contour
of the loops. This is a desirable shape, because it creates multiple
reflection paths
for the light emitted from the first fiber along a length of the loop. The
curved shape
is optimal for transferring light into the second fiber, which bears a
symmetrical
shape relationship to the first fiber.
Single loop pairs as shown in Figures 26, 27 and 28 may be formed by bending
the
fibers into tight loops and pushing them back into surrounding tubing. The end
can
then be dipped in epoxy. At the non looped ends of the fibers, an LED or other
light
source is attached to one fiber for illumination, and the other fiber is
attached to a
photodiode and amplifier or other similar photodetection system. The cut end
of
CA 02307468 2000-OS-03
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each fiber near the sensing loops may be of any length, and can be extended to
provide other signaling functions or to create other loop structures along the
same
fiber. Normally, however, it is cut 5 to 10 mm away from the loop. If desired,
it may
be covered with opaque material to prevent ingress or egress of light.
An array according to the present invention may be used in conjunction with
other
devices. The optical sensor may be instrumented by attaching at least one
fiber (a
"first" fiber) from each pair to a light source, and the other fiber (the
"second" fiber)
to an individual photodetector.
An array may also be multiplexed. For example, according to the above, an
array
o may be used in a multiplexer whereby multiple first fibers are attached to
each of
several light emitting diodes (LEDs), and multiple second fibers are attached
to each
of multiple photodetectors. The fibers are arranged so that, for instance,
four fibers
from the first four looped or bent pairs of the array are illuminated by a
first LED and
the second looped or bent pair mates are read out by 4 photodetectors. The
same 4
photodetectors are used to read out other pairs when they become illuminated
by
turning off the first LED and turning on another. This system may be extended
to
multiplex any number of loops. A typical multiplexer is arranged to have 6
LEDs and
8 photodiodes, with 8 fibers at each LED and 6 fibers at each photodiode, for
a 6 X
8 = 48 element array. Alternatively, all loop or bend pairs may be illuminated
by a
2o common source, and read out by a television camera such as a charge-coupled-
device (CCD) camera or a line scanner.
An advantage of an array of discrete point sensors is the absolute accuracy
with
which the location of each loop is known along the substrate. When liquid
first
contacts a sensor pair, its location can be known with great accuracy.
However, the position of liquid between point sensing pairs in an array is not
known.
This may be resolved by using another, continuous sensing means in conjunction
with the array. The result can be a very accurate sensor combination. For
example,
a tank instrumented with a conventional pressure sensor has an approximate
range
CA 02307468 2000-OS-03
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of 1 % accuracy over the range of pressures due to changes in tank level. By
combining the pressure sensor with an array of 16 optical point sensors
according to
the present invention, spaced equally over the height of the tank, the
accuracy can
be improved to as good as 1/16%, using a computer to re-calibrate the pressure
sensor automatically every time the liquid level passes the accurately known
position of one of the optical sensors. Similarly, 48 optical sensors could be
used to
obtain an overall accuracy of 1 /48% = 0.02%.
As illustrated in Figure 31, an array, for example as illustrated in Figure
30, may
o also be used in conjunction with a standpipe inside the tank open at the
bottom of
the tank, and a means of varying the pressure locally within the standpipe to
change
the height of liquid within it. The control of local pressure requires only a
small
added pressure, as one need only vary the height by one inter-sensor distance.
By
reading the pressure over a span of one intersensor length of the array,
combined
with knowledge of the liquid location to the nearest intersensor interval, an
instrumentation system can determine the actual liquid height before
pressurization
with excellent accuracy. For example, with the provision of a 48 element array
and a
1 % pressure sensor, an accuracy of 1/48 percent is easily achieved over the
total
height of the tank.
2o If desired, rather than use pressure to displace the liquid, one can also
move the
array up and down by known amounts to read the exact height of the liquid. A
major
advantage is that the array need not be moved by more than one intersensor
length
to determine the liquid height within the entire height of the tank. For
instance, if
there are 48 elements to the array, and the tank is 48 feet tall, there is no
need to
move the array more than 1 foot to determine the liquid height to great
accuracy.
An array of lenticularly coupled fiber sensors, each of which has multiple
sinuations
may also be used to obtain highly accurate measurements of liquid height. Each
member of the array can be made to have a throughput that decreases by 1/n
each
time liquid covers one of the n sinuations in each member so that the member
has a
3o throughput near zero when fully covered. An array of 48 members, each with
10
CA 02307468 2000-OS-03
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sinuations, can have an absolute accuracy of 0.2 percent.
In an alternative embodiment, the sensor may be used as a humidity sensor. In
use
one may detect the humidity in one's breath by breathing on the loops. As
such, the
device may be used as a small, rapid all optical humidity sensor substitute
for a
chilled mirror humidity sensor. Traditionally, one would chill the mirror to
detect dew-
point. By chilling the loops one would be able to detect dew-point.
In a further alternative embodiment, a lenticularly coupled sensor with pre-
formed
curves that couple light between the fibers, may be used as a pressure sensor.
According to the present alternative embodiment, the optical sensor includes a
pair
0 of fiber optic fibers, having a film, i.e., plastic or the like, placed
against the loop or
lens and pressure is then exerted on the film. Preferably the plastic film may
be
clear, colored or dark, and may even be opaque. Since the film is to some
extent
deformable, it will act as a frustrator (having an index higher than air, or
in the case
of dark tapes, simply an absorber) whose contact area varies with pressure.
Performance is not affected by thickness of the contacting film. For example,
films
like 10 mil polyethylene, 4 mil mylar, 1 or 2 mil Scotch tape, black or
colored vinyl
tape and the like all produce similar results. This present alternative
embodiment is
a true index-based frustrator, not affected by light or dark colors on the
other side of
the film from the loops. A linear array of pressure sensors built according to
this
2o alternative embodiment, with a continuous sheath of flexible plastic
between it and
surrounding liquid, could be used to sense progress of the liquid along its
length,
according to the array members contacted by the plastic as the liquid
advances,
pushing the plastic against the members.
In a further alternative embodiment, a lenticularly coupled sensor without pre-
formed
curves may be placed between two flexible indenting plates, such as waffle-
patterned rubber sheets, plastic or metal screening, plates with holes or
ridges, or
the like. Pressure applied to the sheets will cause bending of the fibers and
thus
coupling of light between the fibers. The throughput of the sensor will be a
measure
of the applied pressure or force, and can be used to classify impressed
pressure
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pattern shapes according to the curvatures imposed and the characteristic
response
designed into the sensor by various methods of creating enhanced coupling
zones.
In a further alternative embodiment shown in Figure 32, a pressure sensor
array
may be formed from multiple parallel fibers (fiber optic ribbon cable), by
forming
lenticular coupling regions 90 between adjacent fibers. If one coupling region
per
pair of fibers is formed, at a known position along the fibers, then the array
may be
used to sense magnitude and location of imposed pressure fields. Each coupling
region may be formed by applying a clear flexible material so that it forms
into a
lenticular shape during curing, as explained previously. Coupling at lower
1o curvatures may be enhanced by creating loss and collection zones under the
lenticular structure. If the array is sandwiched between flexible indenting
plates,
such as waffle-patterned rubber sheets or screens, applied pressure will cause
the
fibers to bend and to couple light wherever a bend falls on a coupling region.
Light
sources 91 and detectors 92 may be placed at opposite ends of the ribbon, or
reflectors may be applied to one end of the fiber ribbon, and all sources and
receivers may be located at the other end. If reflectors are applied at one
end of the
cable to both receiving and transmitting fibers, then each coupling zone will
couple
direct and reflected light, resulting in a larger throughput.
In a further alternative embodiment, a device including the paired optical
fibers and
20~ lens would be quite sensitive to chemically activated gels or the like. If
desired, a
sensor could be used to allow for the detection of chemicals, for use as a
chemical
or biological activity detector or the like.
Additionally, the device in accordance with the present invention could
include a
formed lens constructed from a material including dissolvable substances, such
as a
meltable wax, hot glue or the like. Such a sensor would be adapted to detect
high
temperatures or have the lenses dissolve in the presence of solvents.
As discussed earlier, coupling across a lenticular zone may be enhanced by
treating
the fibers to lose and collect light, by methods such as abrasion or notching:
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"enhancement by treatment". Another enhancement means is to cover the
lenticular
zone with a reflective material such as vacuum deposited metal, adhered metal
foil,
reflective paints, epoxies, liquids, glasses, or thin films. Enhancement by
means of
a reflective layer will be referred to as "coupler mirroring". Enhancement by
coupler
mirroring alone can increase the throughput and reduce the effects of
surrounding
media. It will also tend to reduce light loss from the coupling zone over a
wider
range of curvatures, because internal reflections will tend to be independent
of the
angle of incidence of internal light with the outer surface. Enhancement by
treatment can be used to reduce the curvatures at which coupling will occur.
o Sufficient treatment can produce coupling at zero curvature. However, a
preferred
method is to treat less and to also employ coupler mirroring, with both lens
and
mirrored surface surrounding both sides of the fibers. This has the effect of
reducing the Ai terms of equation 2, so that coupling terms Ki predominate.
The
throughput is raised for straight fibers so that a bipolar sensor is easily
produced;
one that has decreasing throughput for bends of one polarity and increasing
throughput for the other polarity. It is possible to make sensors that have a
linear
relationship between curvature and transversely coupled throughput. Single-
fiber
bend sensors have a drop in throughput when the treated zone is convex outward
('negative curvature polarity'). Transversely coupled bend sensors that
include
2o coupler mirroring and loss treatment have an increase in throughput for
negative
curvature polarity.
Consideration is now given to the case where a lenticularly coupled pair of
fibers
has source and detector at one end of the pair and mirrored ends at the other
end of
the pair. Mirrored ends may be formed by conventional means such as vacuum
deposition of metals, adhesion of metal or other reflective material, adhesion
of
microprisms, or prismatic cutting of the ends. Such a structure is shown in
the
perspective view of Figure 33, with a single, discrete lenticularly coupled
zone. The
lenticularly coupled zone may take on all the forms already discussed,
including
long, distributed; short, discrete; pre-bent; enhanced by 'loss' zones; not
enhanced;
30 lenticular on one side; lenticular on both sides; mirrored; or not
mirrored. In all
cases, light will couple transversely across the lenticular zone, according to
the
CA 02307468 2000-OS-03
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conditions of bend, loss treatment, and surrounding media. The structure of
Figure
33 is the same as that of Figure 6 except for mirrored ends 111 and 113. The
mirrored ends enable some new features. Light may now propagate across the
coupling zone in both directions and be detected by the same detector. There
is a
'direct' path, indicated by the figure numbers 101, 102, 103, 104 and 105; and
a
'reflected' path indicated by the figure numbers 101, 106, 107, 108, and 109.
Either
end mirror may be removed and a detection path will remain, but when both
mirrors
are used there is more light. In Figure 33 the fibers are shown splayed apart
to
emphasize that the mirrors are separate so that the only coupling is across
the
o lenticular coupling zone. In practice, the mirrored end portions of the
fibers may be
adjacent and touching, or touching but with the mirrors displaced axially. In
a
preferred embodiment, the structure of Figure 33 is a discrete curvature
sensor, with
adjacent mirrored ends, 0.5 mm diameter plastic optical fibers each treated to
lose
light in narrow adjacent strips 12 mm long, covered with a lenticular
structure 110 of
clear flexible epoxy surmounted with reflective foil. The source fiber 14 is
powered
by an LED with its optical output maintained constant in a control circuit;
the
detector fiber 15 is connected to a photodiode and transimpedence amplifier
with an
output voltage proportional to intensity of throughput light. A surface-
treated area is
indicated at 115. The following have been measured for such a structure:
2o Throughput approximately doubles if both fibers are mirrored at the ends
compared
to only either one of the fibers. Without the mirroring on the lenticular
coupling
structure, throughput increases for negative bends (treated side convex
outward),
and decreases, but slightly, for positive bends. With the coupler mirroring,
the
throughput more than doubles and the response curve is truly bipolar and
approximately linear. Modulation is approximately +/- 20% of throughput
intensity
for curvatures of +/-6 cm radius, with maximum throughput for negative bends.
The same structure of Figure 33, without the coupler mirroring, becomes a
pressure
sensor if placed between two pieces of plastic screen with a mesh size of
approximately 10 squares per cm. The plastic mesh is used to produce
3o microbending and hence coupling between the fibers due to light lost into
the
CA 02307468 2000-OS-03
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lenticular structure. Pressure sensing of this sort may also be effected with
the
lenticular coupler but without the loss treatment. Typical output is a 10%
increase in
throughput for a pressure of 1 pound per square inch. The output may be
increased
by using metal bands such as'/d' x 0.005" spring steel on the sides of the
screens
facing away from the fibers.
The same structure of Figure 33 may be extended to perform the same long-fiber
shape sensing and liquid detection tasks described elsewhere in this
disclosure for
sensors not having reflectors on the fiber ends.
In a further variation on the structure of Figure 33, a third fiber is added
on the other
o side of the source fiber, adjacent to it so that all fibers lie in a plane.
The third fiber
is used as a second detector fiber, fitted with another optical intensity
detector.
Transverse coupling may be effected into either detector fiber at the same
axial
location or at separate axial locations. If coupler mirroring and loss
treatment are
applied, the attenuation terms) Ai of eq. 2 will vary insignificantly with
bending, so
that each detector fiber may be used to measure either a different aspect of
bending
at the same location, or another bend at a different axial location. Examples
of
'other aspect of bending' include bending sensed with a different linearity or
polarity
response, so that three fibers can be used to discriminate classes of shapes.
In
another embodiment, the fibers are arranged so their centers fall on corners
of a
2o triangle in cross section, rather than a line. A first set of loss
treatment strips is
applied so that light is coupled transversely from the source fiber to the
first detector
fiber along a side of the triangle. A second treatment is applied so that
coupling
occurs between the source fiber and the second detector fiber along another
side of
the triangle. A lenticular layer surrounds the entire structure or at least
the coupling
zones. Such a structure can sense bending along different axes, and be
calibrated
to become an 'X-Y' bend sensor, used to resolve a plane of maximum bending
applied to the structure by a lateral force. To permit bending of the
triangular
structure, it may be constructed with somewhat extensible materials and/or
twisted
to form a spiral triangular structure. Larger arrays may be formed with
multiples of
3o the planar or triangular triads above. A larger planar array appears in
Figure 32 in
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non-mirrored form, but the mirrored form is of course possible.
Figure 34 is a schematic diagram of a lenticularly coupled fiber optic sensor
as in
Figure 33, but with multiple discrete coupling zones 84, 86, 88, 90. Each
coupling
zone may be made with the various treatments, mirroring, extents, and other
variations discussed elsewhere in this disclosure. In this Figure mirrors are
shown
at 94, 96. In order to resolve responses at the detector due to deformations
or
interactions at each coupling zone, each coupling zone is made wavelength-
dependent and the source fiber is illuminated with light of more than one
wavelength, such as with white light, light from multiple LEDs, or a 'chirped'
laser.
o Zones are made wavelength dependent by conventional means used to produce
wavelength-dependent transmission or reflection. Means include coloring the
lenticular medium with dyes, diffractive inclusions, or absorbers. Means also
include coloring the reflective layer to be wavelength dependent, or using a
dichroic
thin-film reflective layer. Wavelength-selective detectors may be used at the
detector end of the detector fiber, so that each detector responds to each
coupler
and not to the others. Means include detectors fitted with dichroic or colored
filters,
automated monochromators, diffraction grating spectrometers, and other
conventional techniques.
Using the same terminology as that for eq. 2, one can express the throughput
of the
2o structure of Figure 34. The first coupler, 84, has a direct path with
throughput
Ecd=K1xA2xA3xA4xA4xA3xA2xA1,
and a reflected path throughput
Ecr=K1xA1xA2xA3xA4xA4xA3xA2
Ecd and Ecr are the same. In fact, each coupler has an equation of similar
form, so
that for each coupler in this example:
Ec1=2xK1A1 x A2~2 x A3~2 x A4~2, where Ai~2 is Ai x Ai.
Ec2=2xK2A2 x A1 ~2 x A3~2 x A4~2
Ec3=2xK3A3 x A1 ~2 x A2~2 x A4~2
Ec4=2xK4A4 x A1 ~2 x A2~2 x A3~2
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We wish to calibrate this system so that by measuring the separate Eci for
each
coupler, we may calculate Ki for that coupler, where Ki is the coupling factor
due to
an external influence (shape, pressure, contact, etc.). This is possible
because in
each case Eci=KiAi~Aj~2, where the product is over all A's except Ai for that
coupler. The Ai can be taken to be constants if a reflective layer is used
over the
lenticular layer, in which case Eci=KiGi, where Gi is a constant associated
with
coupler i. If the Ai vary with bending, solutions are possible using recursive
methods based on knowledge of the variations in Ai with bending for each
coupler.
An example of a wavelength-specific coupled structure used to make a three-
~c~ dimensional bend and twist sensing structure as described (Danisch, 9F028-
7-
7153/01-SW) in the prior art, but now with only two fibers used to form the
complete
array, is given in Figure 35. The five coupled zones 84, 86, 88, 90, 92 are
arranged
at approximately 45 degrees to the axis of the common substrate 97 so that
each
senses a component of bend and twist. Once the curvature at each coupler is
known, bend, twist, and full three dimensional Cartesian shape are given in
the prior
art referenced above.
Strong advantages may be cited for sensor structures built with reflectors at
the
ends:
- Source and detector may be located at a single end of the structure.
20~ - Because no turn-around loops are necessary, the sensors may be built
in long lengths and then cut to shorter lengths. End reflectors may be
applied by thin film deposition, adhesion, spraying, or other low cost
automated techniques.
- The structure may be as narrow as the fibers involved, with no
additional space required for a turn-around loop.
Further advantages result from reflectors at the coupling zones. For bend
sensors,
these act as optical buffers from external influences such as liquids and
ambient
light. The throughput is doubled, including modulated throughput, and less
3o treatment is required to produce a bipolar bend sensor.
CA 02307468 2000-OS-03
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As described above, single fibers, among other uses, enable the
classifications of
deformations. Thus, using two individual fibers, each treated differently to
the other,
such that each fiber produces a signal variation which is a product of the
form of
deformation. Thus, for example, one fiber can be treated such that it is
particularly
sensitive to long, relatively shallow deformations, while the other can be
treated
such that it is particularly sensitive to sharp-edged deformations. If applied
to an
automobile door, for example, and with the output from the fibers fed to a
comparator, classification of the shape of the deformation can be obtained.
This
can be used to decide whether the deformation relates to a collision which
warrants
safety system actuation. Such fibers can be positioned in seats to determine
whether the seat is occupied. If unoccupied then actuation of an air bag or
other
safety system is unnecessary. A seat application can be used also to determine
the
weight of an occupant, either preventing, or modifying, actuation of an air
bag if the
seat is occupied by a child or other small person. Many other uses can be
considered.
Further, more complex classification can be obtained by using more than two
fibers.
For example, in a multiple fiber arrangement, while some of the fibers may
have the
same treatment, their orientation can be varied, to provide some directional
information regarding the deformation - giving what could be termed a "3D"
result.
20~ Depending upon the information desired concerning the form, or shape, or
size of a
deformation, or any combination thereof, so a plurality of fibers can each
have
different treatments, or there can be combinations of fibers having different
treatments and fibers having the same treatments but differently orientated. A
common input can be used, but a separate detector is used for each fiber, the
outputs being combined in a comparator for providing classification of the
deformation.
The treatment of the fibers can vary, typical examples being abrasion,
chemical
treatment, heat forming and notching. The type or form of treatment will vary
in
accordance with the particular form of deformation to be sensed, for example,
so coarse or fine notching, or abrasion. One form of treatment will be for
monitoring
CA 02307468 2000-OS-03
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short sharp deformations and another form of treatment for longer, more
gradual
deformations.
In alternative embodiments, the device in accordance with the present
invention
could include a single fiber shape sensor for air bag or other safety system
deployment decisions, including whether or not to deploy, at what pressure to
deploy, based on a class of shape of an object striking a portion such as the
front,
sides or rear of a vehicle.
In a further alternative embodiment, the device in accordance with the present
invention could include a single fiber shape sensor for determining a seat
occupant
o weight, position and shape for purposes of safety system deployment
decisions,
including detection of an occupied child safety seat. Decisions for any of the
above
embodiments could be based on suitable methods and or programs, for example,
algorithms in an electronic control system of a vehicle.
In an additional alternative embodiment, the device in accordance with the
present
invention could include a single fiber shape sensor installed in a window,
door or
tailgate gasket or positioned in another suitable location, in order to detect
if a hand
or other body part if present. If such a body part is detected, the closure of
the door,
window or the like member would be interrupted.
In a further preferred alternative embodiment, the device in accordance with
the
2o present invention could include a single fiber shape sensor for detecting
contact and
the shape of contact between a car bumper or other vehicle, i.e. cars, trucks,
constructions vehicles, front end loaders, boats, boat bumpers, loading docks,
marine docks and other suitable surfaces where such a sensor would desirably
be
placed for detecting contact and shape of contact.
In another alternative embodiment, the device in accordance with the present
invention could include a single fiber shape sensor for use in an alarm
system, for
example as an intrusion alarm on a threshold, under a rug, or other like
object, or in
CA 02307468 2000-OS-03
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a window or door structure.
In an alternative embodiment, the device in accordance with the present
invention
could include a single fiber shape sensor for a safety mat, to actuate or de-
actuate a
machine when a person steps on or off the mat.
In an alternative embodiment, the device in accordance with the present
invention
could include a single fiber shape sensor for use as a pressure detector
buried in
pavement or on pavement, to detect and measure vehicle wheel presence, shape,
speed and numbers. Alternatively, according to the above, the single shape
sensor
could be used to detect, in a tire, under- or over-inflation, shape of the
area of
o contact of the tire with the road, or the shape of any portion of the tire.
In a further alternative embodiment, the device in accordance with the present
invention could include a single fiber shape sensor for use in a bed or chair,
for
detection of occupant position, weight, shape and other data for purposes of
position adjustment, patient monitoring or sleep research.
In an alternative embodiment, the device in accordance with the present
invention
could include a single fiber shape sensor for use to detect contact and the
force of
contact in a target, such as a gaming target, gaming tool or military target.
This
would allow for measurement or detection of contact and force of contact of a
ball,
projectile or other like device.
2o In an alternative embodiment, the device in accordance with the present
invention
could include a single fiber shape sensor for use in safety research, such as
in or on
the deformable elements of a crash-test dummy, i.e., in or on the deformable
abdomen, chest or head of a crash-test dummy, to measure shape and severity of
an impact.
In an alternative embodiment, the device in accordance with the present
invention
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could include a single fiber shape sensor in an elevator to detect the
presence of an
obstruction between the door or closing strips of the elevator doors.
In a further alternative embodiment, the device in accordance with the present
invention could include at least one fiber in a shape sensor adapted to detect
the
shape of frontal impacts for purposes of safety system deployment.
As those skilled in the art will realize, these preferred illustrated details
can be
subjected to substantial variations, without affecting the function of the
illustrated
embodiment. Although embodiments of the invention have been described above,
it
is not limited thereto and it will be apparent to those skilled in the art
that numerous
o modifications form part of the present invention insofar as they do not
depart from
the spirit, nature and scope of the claimed and described invention.
