Note: Descriptions are shown in the official language in which they were submitted.
20304~'8
A DISPLACEMFNT DIRECTION AN~ AMPLITU~E SENSOR
BACKGROUND oF T~ INVE~TIQN
The present invention relates to the measurement of
direction and ampli~ude of small displacements.
The invention applies to measurement of wind force
and direction, that is, to the manufacturing of a speed
and direction anemometer; measurement of a fluid flow;
detection of displacement applied to a remote control
stick, for example a joy-stick for electronic games, etc.
SUMMA~Y OF THE L~VENTIO~
An object of the invention is to provide such a
sensor which is particularly simple and compact.
Another object of the invention is to provide such a
sensor which is substantially insensitive to electron-ic
interferencest such as atmospheric interFerences.
A further object of the invention is to provide such
a sensor which is usable in very strict temperature and
dampness environments, and especially little sensitive to
frost and can therefore be used in mountains or on sea.
A yet further object of the invention is to provide ~;
for a manufacturing mode of such a sensor.
The invention makes use of a sensor whose operation ~;
principle is disclosed, for another purpose, in Applied
Optics, Vol. ~4, No. 15, August 1, 1~85, Johnson et al.
SpeciFically, the invention provides a direction and
amplitude sensor for detecting displacement comprising a
mirror integral with a mobile element and a photoemitter
and photoreceptor assembly integral with a reference
frame; this assembly comprises a central optical fiber
emitting a light cone towards the mirror and receiving
optical fibers, each of which is in contact with the
central fiber; the mirror is circular and its diameter
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and its axial distance from the extremity of ~he fibers
are such, in centered position, that its diameter
substantially corresponds to that of the light cone
generated by the central fiber and that the reflected
light cone i5 substantially tangent to the external
radial edges of the receiving fibers. The mirror is
fitted on the end transversal wall of a tube, perpen-
dicularly to the axis of this tube and centered there-
with, the other extremity of this tube being embedded in
a frame, the optical fib~rs having their extremities
inside said tube and oriented towards the mirror.
According to an embodiment of the invention, the
light emitted by the central optic fiber originates from
an electroluminescent diode.
According to an embodiment of the invention, the
emitting and receiving fibers have the same diameter, six
receiving fibers being provided.
According to an 0mbodiment of the invention, the
emitting and receiving fibers are index skipping fibers,
~0 the extremities of which are bare and joined side by
side.
According to an embodiment of the invention, the
optical fibers are arranged inside a second tube arranged
inside the first tube and integral with the support.
According to an embodiment of the invention, the
extremity of the first tube opposite to its embedded
extremity is prolongated by an arm submitted to an
external force.
According to an embodiment of the invention, the
external wall of the tube or of the arm is submitted to
the action of a fluid flow, whereby said sensor consti-
tutes a speed and direction anemometer or a flow-meter.
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According to an embodiment of the invention, the
extremity cf the arm is fitted with holding means,
whereby the sensor constitutss a joy-stick.
According to a further aspect of the invention, a
process for manufacturing the above described sensor com-
prises the following steps: assembling the various
components of the sensor in said ~ube, providing the
bottom of the tube with a transparent window coated with
a reflecting layer and a photoresist, irradiating khe
resist from the central fiber by a light beam having a
wavelength passing through said reflecting layer, etching
by means of conventional etchants the photosensitive pro- -
duct and the reflecting layer so as to delineate a mirror
corresponding to the irradiated region.
BBI~F P~ BI~IIQ~ QE I~ QR~
The foregoing and other objects, features and advan-
tages of the invention will be apparent from the
following detailed description of a preferred embodiment
as illustrated in the accompanying drawings wherein: ~
Fig. 1 is a perspective view for illustrating the ~ ;
principle of a sensor in rest position;
Fig. 2 is a view analogous to Fig. 1, when the sensor
detects a displacement;
Fig. 3 is an end view of the fiber bundle of Figs 1
and 2;
Fig. 4 illustrates an exemplary mounting of a sensor
according to the invention;
Figs 5A and 5B illustrate two successive manufactur-
ing steps of a sensor according to the invention; and
Figs 6A and 6B illustrate two successive manufactur-
ing steps of a sensor according to the 1nvention.
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DETAILED.DESC.B.I.PIIQN.~ F...T.HE~.I.NY~ JIIs;)N
Fig. 1 is a perspective view for illustrating the
principle of a sensor useful to the invention comprising
seven identical optical fibers 1-7. Fibers 2-6 surround
the central fiber 1, that is, each fiber 2-7 contacts, at
least at its extremity1 the central fiber 1 and two of
the adjacent peripheral fibers.
Those seven fibers are cut away so that their
extremities are substantially arranged in a same plane
orthogonally to their axis. The othar extremity of the
central fiber 1 is associated with a photoemitter (not
shown) and the other extremity of each fiber 2-7 is
associated with a photodetector (not shown).
The light beam from fiber 1 is directed towards a
circular mlrror 10 which, at rest, is centered on the
axis of the fiber 1 and orthogonally to the latter. The
size of this mirror 10 is determined so as to correspond
to the intersection of its plane with the light cone 11
generated by fiber 1. The distance between the plane of
mirror 10 and the end plane of fibers 1-7 is such that
the light cone 12 reflectsd by this mirror cuts the end
plane of the fibers according to a circle 13 circum-
scribed to useful regions (core~ of the fibers 2-7 (see
Fig. 3). Thus, in this configuration, all the extremities
of the receiving fibers are entirely lighted and receive
the same amount of light.
Fig. 2 shows the case when the mirror 10 has been
shifted towards the right with respect to its rest
position of Fig. 1. The light cone generated by the fiber
1 is not modified and only a portion of the mirror 10 is
lighted while the fibers arranged on the left on the
figure (fibers 2, 3 and 7) are only partially lighted and
the fibers 4, 5 and 6 continue receiving the same amount
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20'~0~68
of light. In the top view of Fig. ~, the light spot near
the end plane of the fibers then corresponds to the
intersection of the above mentioned circle 1~ and of a
circle 14 shifted towards the right.
The variations of light intensity on the sensors
associated with fibers 2--1 will then supply an indication
on the amount of displacement of mirror lO as well as on
the direction of this displacement. Processing circuits
and an appropriate program will directly supply inform-
ation on the values of amplitude and direction of the
displacement, as a function of precalculated values or,
preferably, of test results.
In order to obtain satisfactory reproducible
information, it is desirable that the light projected on
the front surfaces of the receiving fibers is homo-
geneous. Thus, it is preferred to inject into the emit-
ting fiber l the light from an electroluminescent diode
(having for example a wavelength of ~50 nm) rather than
from a laser diode. Indeed, in the latter case, the
emitted beam generally comprises speckles.
The above described Figs 1 and 3 are very schematic
and are intended to make clearly understood the operation
of the sensor used in the invention.
Fig. 4 illustrates an embodiment of the sensor
according to the invention. This sensor comprises a frame
20 intagral with a reference frame wherein is embedded a
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cylindric tube 21. This tube can, for example, be made of
stainless steel and can be submitted to a force, the
intensity and orientation of which are to be determined.
The extremity of the cylinder 21 opposite to its
embedding region is closed by a transversal wall 22 which
bears on lts lower surtace the mirror 10, the reflecting
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~` 203~468
surface o~ which i6 downwardly oriented in the
representation of the figure.
The fiber bundle is inserted inside a second tube ~3
integral with the reference frame 20, the extremity of
the fibers being oriented towards the mirror 10.
Thus, when a lateral force is applied to the tube 21,
the latter is deformed and the mirror 10 is essentially
shifted within its plane.
It is possible to used joined bare fibers. Those
fibers can be of the index skipping type, each comprising
a core (drawn in black hatched lines in Fig. 3) and an
external wall. It is possible to choose fibers, the core
of which has a diameter of 100-200 ~m and the external
diameter is 140-280 ~m, respectively, those fibers being
availabl~ on the market. The mirror, the size of which is
chosen as a function of the above given indications, can
have a diameter of about a few hundreds ~m and be at a
distance of a few tenths to a few mm from the extremity
of the fibers. Thus, it will be possible to detect
lateral displacements of the mirror of the order of
magnitude of the fiber diameter, that is, of about one to
a few hundreds ~m. The tube 21 may have a length of a few
tens cm and a wall thickness of a few tenths mm. -
As above indicated, the mirror has to substantially
exactly correspond to the light cone generated by the
fiber 1; however, this mirror may have slightly smaller
sizes, wh1ch only changes the calibration of the system
and the amplitude of the observable displacements. But,
if the mirror has a larger size, there will be a dead
zone at the beginning of the displacement, which may `~
` prove use~ul for certain applications.
Moreover, although it has been previously indicated
that bare fibers are used, it is also possible to use
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optical fibers provided with their usual coating.
However, the use of bare fibers is the embodiment
actually pre~erred by users. Indeed, a fiber assembling
embodiment consists in baring the latter on a length of,
for example, about ten cm, khen to put a drop of glue at
the position of the fiber junction, the latter being
automatically joined together through capillarity to form
an assembly, an extremity of which can be seen in Figs 1
and 2. Then, the extremity of the joined fibers can be
polished again.
Among the advantages of the invention, it can be
mentioned that, due to the limited aperture angle of the
fibers ~usually about 20'), even if parasitic reflections
occur on the edges of the mirror and on the inner walls
of the tube 21, the light resulting from those
reflections and directed towards the receiving fibers
will arrive, according to a high probability, according
to an incidence not accepted by those fibers. Therefore,
there is a natural protection against the parasitic
light.
On the other hand, in the embodiment of Fig. 4, the
whole detection system is protected from ambient
atmosphere by the tube 21 sensitive to the application of
an external force. The inner portion of this tube 21 can
for example be filled with neutral gas.
Moreover, as is conventional when optical fibers are
used for detection, the photoemitter, the photoreceivers
and the associated electronic circuits can be arranged at
a determined distance from the sensor, in an electrically
shielded chamber.
The sensor according to the invention can have
numerous applications.
2030~68
For example, the tube 21 can be inserted by an
airtight sealing in a pipe where it is desired to measure
the flow, the deFormation of the tube being caused by the
pressure of the fluid.
Similarly, the tube 21 can be placed in ambient
atmosphere ln order to be sensitive to wind and to form a
speed and direction anemometer In that case, it is
possible to provide, integrally with the upper portion of
the tube, a component more sensitive to wind such as a
sphere, for example a golf ball.
In an application of the invention, the tube 21 can
be prolongated by a stick or constitute itself this
stick, and the sensor will supply an indication on the
pressures applied to the stick for supplying a remote
control system, for example of the type of video game
joy-sticks.
Of course, the invention is liable to numerous
variants and modifications that will appear to those
skil1ed in the art, especially as regards the nature of
the materials and fibers used. For example, it has been ~
previously assumed that the emitting fiber had the same ~`
external dlameter as the receiving fibers. It can be
devised that those fibers have different diameters. If
the receiving tibers have a diameter smaller than the i`
emitting fiber, it will be possible to place a greater
number of receiving fibers around the emitting fiber and
conversely if the receiving fibers have a larger
diametar.
Moreover, although the receiving f;bers have been
described as being all adjacent, it will be possible to
space them apart, for example by means of neutral fibers.
On the other hand, the case when the mirror 10 is
shifted within its plane has been essentially described. ~ -~
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203~6~8
It is clear that the invention will permit detecting
rotations of this mirror, provided an appropriate
calibration is provided.
According to an aspect of the invention, a process
for manufacturing the mirror 10 present at the bottom of
the tube 21 is provided.
One could devise to provide a mirror manufactured
independently of the tube, for example a fiber with a
metallized extremity inserted in wall 22. However,
critical centering problems arise. More generally, any
manufacturing process wherein the mirror is manufactured
independently of the centering of the internal tube and
light beam supplied by the central fiber will raise in
practice critical problems. This is all the more true ~-
that, when considering practical orders of magnitude, the
mirror will have a diameter of about 300 ~m and will be
at a distance from the fiber beam end of about SO0 ~m.
To solve this problem, it has been suggested to us~,
in order to delineate the mirror, the light cone from the ~- ;
central emitting fiber after positioning optical fibers
in the sensor assembly. Thus, the mirror will be automa~
tically posit;oned in front of the central fiber, which
will avoid resorting to critical adjustment processes.
This type of self-centering process will be described
in relation with Figs 5A-6B and 6A-6B. First, it will be
noted that these figures are not drawn to scale but their ~;
size has been arbitrarily enlarged and reduced to
facilitate the legibility thereof. ~
In these figures, the above described elements are ~;
designated by same references. ~;
Thus, Fig. 5A shows again the external tube 21 with
its bottom 22, and the internal tube 23 containing the
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optical fibers among which the central fiber 1. Two 1ate-
ral fibers 2 and 5 are visible.
On the inner wall of bottom 22 are successively
d0posited a layer 30 forming a mirror, for example a
metal layer made of a1uminum or gold, and a negative
photoresist layer 31 of the type usually used in phoko-
etching. Then, a light beam 32 is emitted from the
central fiber 1 for insolating the resist. During a first
step, the resist is eliminated at the non lighted posi-
tions, then the layer 30 is etched off at these posi-
tions. Lastly, the irradiated resist in the central
portion is removed to let appear the central portion of
the reflecting layer, thus forming the mirror 10 as
illustrated in Fig. 5B. This mirror will then exactly
have the desired size.
The process described in relation with Figs 5A and 5B
gives satisfactory results but implies to proceed to
chemical etching operations inside the tube. For this
purpose, as represented in Fig. 5A, an aperture 34 for
20 introducing and extracting etchants is provided; this
aperture must then be obturated, for example by means of
glue or a welding 35. Moreover, it is generally desirable
that etchants do not contact the front surface of the
optical fibers, which renders the operation very critical
25 due to the small distance between the extremity of the
fibers and the layers to be etched.
Thus, another self-aligned process for manufacturing
mirror 10 has been devised and will be described in rela~
tion with Figs 6A and 6B. In that case, the bottom of the
tube 21 is made of a material transparent for the
wavelengths used, for example a glass window 40. This
window is coated, on the external side of the tube with a
reflecting layer 41 for the wavelengths at which the
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sensor will be used, and with a negative photoresist
layer 42.
According to the invention, a light beam is generated
from the central optical fiber 1 at an active wavelength
for ~he photoresist layer 42, this wavelength being
chosen in relation with the material 41 so as to pass
therethrough at least partially.
For example, if the layer 41 is a thin metal layer,
it will constitute a satisfactory mirror for the working
wavelength o~ the sensor at about 850 nm, which
corresponds to available wavelengths for electro-
luminescent diodes. In order to insolate the resist, a
lower wavelength will be used, for example the blue line
at 488 nm from an argon laser. This beam will effectively
pass through a thin layer of metal such as gold or
aluminum. Once this insolation has been carried out, as
in the case described in relation with Figs ~A and 5B,
the resist at the periphery will first be eliminated,
then the metal layer will be etched so as to form the
mirror lO. The upper resist layer above the mirror will
be eliminated or left in place. Moreover, it will be
possible to deposit a final encapsulation layer in order
to protect the mirror.
The process according to the invention permits, once
the external tube, the internal tube and the fibers are
positioned, to manufacture a perfectly centered mirror 10
without acting inside the chamber defined by the external
tube 21.
As regards the manufacturing method, numerous va-
riants and modifications will appear to those skilled inthe art, especially as regards the materials constituting
the various components of the sensor and the assembly
mode thereof. For example, in the above description in
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12
relation with Fig. 6A, layers 4l and 4Z have been
described as being deposited on the bottom 40 after
assembling. Obviously, these layers could be arranged on
the bottom prior to assembling and, although they are
represented as protruding out of the tube, they cow1d be
arranged so as not to protruda out of the tube or even to
be inse-ted into it.
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