U.S. patent application number 10/142686 was filed with the patent office on 2002-12-05 for trapezoidal coil for fiber optic gyroscopes.
Invention is credited to Gregory, Peter.
Application Number | 20020179760 10/142686 |
Document ID | / |
Family ID | 23114289 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020179760 |
Kind Code |
A1 |
Gregory, Peter |
December 5, 2002 |
Trapezoidal coil for fiber optic gyroscopes
Abstract
A trapezoidal bobbin for providing a foundation for a coil of
optical fiber comprises an elongated hub, an upper flange and a
lower flange. The elongated hub includes a longitudinal axis, a
first end, a second end and an exterior surface. The hub is
symmetrically disposed about the longitudinal axis. The upper
flange is disposed at the first end of the hub, and includes an
exterior surface that is substantially perpendicular to the
longitudinal axis and faces away from the hub. The upper flange is
further includes an interior surface that forms an angle of
substantially 60 degrees with respect to the longitudinal axis. The
lower flange is disposed at the second end of the hub, and includes
an exterior surface that is substantially perpendicular to the
longitudinal axis and facing away from the hub, and an interior
surface forming an angle of substantially 60 degrees with respect
to the longitudinal axis.
Inventors: |
Gregory, Peter; (North
Attleboro, MA) |
Correspondence
Address: |
McDermott, Will & Emery
28 State Street
Boston
MA
02109
US
|
Family ID: |
23114289 |
Appl. No.: |
10/142686 |
Filed: |
May 10, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60290042 |
May 11, 2001 |
|
|
|
Current U.S.
Class: |
242/118.4 ;
242/614 |
Current CPC
Class: |
G01C 19/722 20130101;
B65H 75/148 20130101; B65H 2701/5122 20130101; B65H 2701/18444
20130101; B65H 55/04 20130101; H01F 5/02 20130101; G02B 6/4457
20130101; B65H 54/12 20130101; B65H 2701/32 20130101 |
Class at
Publication: |
242/118.4 ;
242/614 |
International
Class: |
B65H 075/14 |
Claims
What is claimed is:
1. A trapezoidal bobbin for providing a foundation for a coil of
optical fiber, comprising: an elongated hub including a
longitudinal axis, a first end, a second end and an exterior
surface, the hub being symmetrically disposed about the
longitudinal axis; an upper flange disposed at the first end of the
hub, the upper flange including an exterior surface being
substantially perpendicular to the longitudinal axis and facing
away from the hub, and an interior surface forming an angle with
respect to the longitudinal axis; a lower flange disposed at the
second end of the hub, the lower flange including an exterior
surface being substantially perpendicular to the longitudinal axis
and facing away from the hub, and an interior surface forming an
angle with respect to the longitudinal axis.
2. A trapezoidal bobbin according to claim 1, wherein the angle
between the interior surface of the upper flange and the
longitudinal axis is substantially 60 degrees.
3. A trapezoidal bobbin according to claim 1, wherein the angle
between the interior surface of the lower flange and the
longitudinal axis is substantially 60 degrees.
4. A trapezoidal bobbin according to claim 1, wherein the upper
flange and the lower flange are fixedly attached to the cylindrical
hub.
5. A trapezoidal bobbin according to claim 1, wherein the
cylindrical hub, the upper flange and the lower flange form a
unitary component.
6. A trapezoidal bobbin according to claim 5, wherein the unitary
component includes a substantially homogenous material.
7. A trapezoidal bobbin according to claim 1, wherein the upper
flange is symmetrically disposed about the longitudinal axis.
8. A trapezoidal bobbin according to claim 1, wherein the lower
flange is symmetrically disposed about the longitudinal axis.
9. A trapezoidal bobbin according to claim 1, wherein a length of
the exterior surface of the hub, measured from the interior surface
of the upper flange to the interior surface of the lower flange, is
substantially equal to an integral number of diameters of an
optical fiber.
10. A trapezoidal bobbin according to claim 1, wherein the
composition of the hub, the upper flange and the lower flange
includes a substance having a thermal expansion characteristic
similar to an optical fiber to be wound on the trapezoidal
bobbin.
11. A trapezoidal bobbin according to claim 10, wherein the
substance includes plastic.
12. A trapezoidal bobbin according to claim 10, wherein the
substance includes a composite material.
13. A trapezoidal optical fiber coil for use in a fiber optic
gyroscope, comprising: a bobbin having (i) a cylindrical hub
characterized by a longitudinal axis, a first end, a second end and
an exterior surface, the hub being symmetrically disposed about the
longitudinal axis, (ii) an upper flange symmetrically disposed
about the longitudinal axis at the first end of the hub, the upper
flange characterized by an exterior surface being substantially
perpendicular to the longitudinal axis and facing away from the
hub, and an interior surface forming an angle of substantially 60
degrees with respect to the longitudinal axis, and (iii) a lower
flange symmetrically disposed about the longitudinal axis at the
second end of the hub, the lower flange characterized by an
exterior surface being substantially perpendicular to the
longitudinal axis and facing away from the hub, and an interior
surface forming an angle of substantially 60 degrees with respect
to the longitudinal axis; a predetermined length of optical fiber
wound about the bobbin in succeeding layers extending from the
longitudinal axis in a radial direction, wherein the first layer is
disposed upon the exterior surface of the hub in an integer number
of turns of the optical fiber, and each subsequent layer having an
integer number of turns greater than the next preceding layer.
14. A trapezoidal optical fiber coil according to claim 13, wherein
the upper flange and the lower flange are fixedly attached to the
cylindrical hub.
15. A trapezoidal optical fiber coil according to claim 13, wherein
the cylindrical hub, the upper flange and the lower flange form a
unitary component.
16. A trapezoidal optical fiber coil according to claim 15, wherein
the unitary component includes a substantially homogenous
material.
17. A trapezoidal optical fiber coil according to claim 13, wherein
the upper flange is symmetrically disposed about the longitudinal
axis.
18. A trapezoidal optical fiber coil according to claim 13, wherein
the lower flange is symmetrically disposed about the longitudinal
axis.
19. A trapezoidal optical fiber coil according to claim 13, wherein
a length of the exterior surface of the hub, measured from the
interior surface of the upper flange to the interior surface of the
lower flange, is substantially equal to an integral number of
diameters of an optical fiber.
20. A trapezoidal optical fiber coil according to claim 13, wherein
the composition of the hub, the upper flange and the lower flange
includes a substance having a thermal expansion characteristic
similar to an optical fiber to be wound on the trapezoidal
bobbin.
21. A trapezoidal optical fiber coil according to claim 20, wherein
the substance includes plastic.
22. A trapezoidal optical fiber coil according to claim 20, wherein
the substance includes a composite material.
23. A trapezoidal optical fiber coil according to claim 13, wherein
the optical fiber, viewed in a plane intersecting the longitudinal
axis, is arranged in a quadrupolar pattern.
24. A trapezoidal optical fiber coil according to claim 13, further
including a layer of epoxy disposed between the first layer of
optical fiber and the exterior surface of the hub.
25. A trapezoidal optical fiber coil according to claim 11, further
including a layer of epoxy disposed between each adjacent layer of
optical fiber.
26. A trapezoidal bobbin for providing a foundation about which an
optical fiber is wound, comprising: hub means for providing an
elongated form for winding optical fiber, the hub means
characterized by a longitudinal axis, a first end, a second end and
an exterior surface, the hub being symmetrically disposed about the
longitudinal axis; upper flange means for terminating the first end
of the hub, the upper flange characterized by an exterior surface
being substantially perpendicular to the longitudinal axis and
facing away from the hub, and an interior surface forming an angle
of substantially 60 degrees with respect to the longitudinal axis;
lower flange means for terminating the second end of the hub, the
lower flange characterized by an exterior surface being
substantially perpendicular to the longitudinal axis and facing
away from the hub, and an interior surface forming an angle of
substantially 60 degrees with respect to the longitudinal axis.
27. A trapezoidal bobbin for providing a foundation about which an
optical fiber is wound, comprising: a cylindrical hub characterized
by a longitudinal axis, a first end, a second end and an exterior
surface, the hub being symmetrically disposed about the
longitudinal axis; an upper flange disposed at the first end of the
hub, the upper flange characterized by an exterior surface being
substantially perpendicular to the longitudinal axis and facing
away from the hub, and an interior surface forming an angle of
substantially 60 degrees with respect to the longitudinal axis; a
lower flange disposed at the second end of the hub, the lower
flange characterized by an exterior surface being substantially
perpendicular to the longitudinal axis and facing away from the
hub, and an interior surface forming an angle of substantially 60
degrees with respect to the longitudinal axis; wherein the
cylindrical hub, the upper flange and the lower flange form a
unitary component, and a length of the exterior surface of the hub,
measured from the interior surface of the upper flange to the
interior surface of the lower flange, is substantially equal to an
integral number of diameters of an optical fiber
28. A method of winding a optical fiber about a trapezoidal bobbin
having (i) a cylindrical hub characterized by a longitudinal axis,
a first end, a second end and an exterior surface, the hub being
symmetrically disposed about the longitudinal axis, (ii) an upper
flange symmetrically disposed about the longitudinal axis at the
first end of the hub, the upper flange characterized by an exterior
surface being substantially perpendicular to the longitudinal axis
and facing away from the hub, and an interior surface forming an
angle of substantially 60 degrees with respect to the longitudinal
axis, and (iii) a lower flange symmetrically disposed about the
longitudinal axis at the second end of the hub, the lower flange
characterized by an exterior surface being substantially
perpendicular to the longitudinal axis and facing away from the
hub, and an interior surface forming an angle of substantially 60
degrees with respect to the longitudinal axis, comprising: winding,
via a first feed spool, a first layer of optical fiber about the
hub from the upper flange to the lower flange, such that the first
layer includes a first integer number of turns of the optical
fiber; moving the first feed spool in a direction parallel to the
longitudinal axis to a location away from the first layer of
optical fiber; winding, via a second feed spool, a second layer of
optical fiber about the hub overlaying the first layer of optical
fiber, from the upper flange to the lower flange, such that the
second layer includes a second integer number of turns being equal
to one more than the first integer number of turns; winding, via
the second feed spool, a third layer of optical fiber about the hub
on top of the second layer of optical fiber, from the lower flange
to the upper flange, such that the second layer includes a third
integer number of tuns being equal to one more than the second
integer number of turns; moving the second feed spool in a
direction parallel to the longitudinal axis to a location away from
the third layer of optical fiber; winding, via the first feed
spool, a fourth layer of optical fiber about the hub on top of the
third layer of optical fiber, from the lower flange to the upper
flange, such that the fourth layer includes a fourth integer number
of turns being equal to one more than the third integer number of
turns.
29. A method according to claim 28, further including repeating,
after winding the fourth layer of optical fiber, the winding of the
first layer, second layer, third layer and fourth layer, so as to
apply at least two sets of four layers on the trapezoidal
bobbin.
30. A method according to claim 28, further including arranging the
layers of optical fiber so as to create a quadrupolar pattern when
the layers are viewed in a plane intersecting the longitudinal
axis.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/290,042 entitled "TRAPEZOIDAL COIL FOR FIBER
OPTIC GYROSCOPES" filed on May 11, 2001, the disclosure of which is
entirely incorporated herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable
REFERENCE TO MICROFICHE APPENDIX
[0003] Not Applicable
BACKGROUND OF THE INVENTION
[0004] The present invention relates to fiber optic gyroscopes
(hereinafter referred to as "FOG"), and more particularly, to
structures that support and stabilize the coils of optical fiber
within a FOG.
[0005] A FOG is used to measure the rate of rotation of a vehicle
or other host platform to which the FOG is attached. The FOG
typically includes a coil of optical fiber that is wound about a
bobbin. The coil, along with the bobbin foundation, can rotate
about an axis of rotation. A light source transmits light into each
end of the optical fiber, so that two light transmissions propagate
through the optical fiber in counter rotating directions. Detection
circuitry, typically residing within an Integrated Optical Circuit
(hereinafter "IOC"), receives the light transmissions as they
emerge from the ends of the optical fiber and measures the relative
phase relationship of the light. The phase relationship of the two
light transmissions is related to the angular rotation of the FOG
coil about the axis of rotation, and may be used to derive an
output that is indicative of the rate of rotation of the FOG
coil.
[0006] FIG. 1A shows a perspective view of a typical prior art
bobbin, and FIG. 1B shows the prior art bobbin of FIG. 1A in
cross-section view. The bobbin 10 is cylindrically shaped and has
an upper flange 12 and a lower flange 14 disposed on opposite ends
of the bobbin. The bobbin 10 further includes a principal axis AX,
that is perpendicular to the planes formed by the outer surface of
the upper flange 12 and the outer surface of the lower flange 14.
The principal axis AX is an axis of rotation about which the bobbin
and optical coil assembly rotate. The upper and lower flanges are
typically characterized by constant thickness, and fabricated as
thin as practical, to maximize the volume available for optical
fiber.
[0007] To stabilize the optical fiber on the bobbin so that the FOG
can operate in high vibration environments, the optical fiber is
often wound onto the hub with an epoxy adhesive between the hub and
the first layer, and also between subsequent layers of optical
fiber. Once the optical fiber is completely wound onto the bobbin,
the coil assembly is placed in an elevated temperature to cure the
epoxy. Because the optical fiber restrains expansion of the coil in
the radial direction, the thermal expansion of the coil is greater
in the axial direction than in the radial direction. Large thermal
induced stresses are therefore produced in the bobbin material and
fiber pack when the bobbin is exposed to a temperature different
from the epoxy curing temperature, which is the minimum stress
temperature of the coil. The effect of changing the temperature of
the coil is best illustrated by a finite element model in FIG. 2,
which shows the predicted stresses generated in a bobbin
manufactured to a prior art. In this example, the zero stress
temperature is +85 degrees Celsius and the stresses are calculated
at the lowest operating temperature of the coil -54 degrees
Celsius. Due to the relatively large thermal expansion of the
epoxy, at temperatures below the zero stress temperature, the
bobbin flanges are placed in bending, generating large stresses in
the flange at the interface with the hub.
[0008] A disadvantage with the prior art bobbin configuration shown
in FIG. 1A is that the flanges 12, 14, extend from the bobbin 10
without supplemental structural support. Further, since the prior
art flanges 10, 12 are typically relatively thin to maximize the
volume available for the optical fiber, these flanges have deformed
and cracked as a result of thermal induced stresses. Further, the
thin prior art flanges are typically characterized by natural modes
of vibration at relatively low frequencies. These low frequency
modes of vibration result in susceptibility to the shock and
vibration environments the host platform experiences.
[0009] To meet performance requirements over temperature, the
optical fiber coil used in fiber optic gyroscopes is often wound in
a quadrupolar pattern. For optimum thermal compensation, the total
number of layers is a multiple of four. Although other winding
patterns may be used, the winding process typically involves the
winding of a predetermined length of optical fiber equally onto a
first feed spool and a second feed spool, so that the midpoint of
the optical fiber occurs between the two feed spools. Winding
commences at the midpoint of the fiber and the first layer is wound
using the first feed spool. For the quadrupolar pattern, the second
layer and the third layer are wound using the second feed spool,
and the fourth layer is wound from the first feed spool. This
four-layer pattern is repeated until the requisite number of layers
has been wound onto the coil. Adaptations of this winding process
involve methods in which the fiber transition occurs between two
non-adjacent layers, for example between the first layer and the
fourth layer. Another disadvantage with the prior art bobbin
configuration stems from the fact that the flanges 12, 14 extend
perpendicularly from the bobbin 10. Some automated coil winding
systems require the bobbin to have a slot in each flange that
extends in a radial direction from the principal axis to the outer
edge of the flange. These slots are both costly to machine and
significantly reduce the stiffness and hence stability of the
bobbin. A guide wheel carries the fiber from the feed spool to the
bobbin. To ensure precise placement of the fiber and to minimize
fiber crossovers, the guide wheel must be situated close to the
fiber layer being wound. With bobbins of the previous art (having
parallel flanges as shown in FIG. 1A) the fiber from the idle,
non-winding feed spool must temporarily exit the slot to prevent
interference with the guide wheel. The fiber from the idle feed
spool is thus "parked" in a position outside the flange until that
feed spool is required for winding, at which time the feed spools
change places, and the previously-active feed spool is parked while
the previously-idle spool winds its fiber onto the bobbin. This
process continues, with the feed spools alternating, until the
fiber coil is completed.
SUMMARY OF THE INVENTION
[0010] In one aspect, a trapezoidal bobbin for providing foundation
for a coil of optical fiber comprises an elongated hub, an upper
flange and a lower flange. The elongated hub includes a
longitudinal axis, a first end, a second end and an exterior
surface. In one embodiment, the hub is cylindrical, although other
elongated shapes may also be used. The hub is symmetrically
disposed about the longitudinal axis. The upper flange is disposed
at the first end of the hub, and includes an exterior surface that
is substantially perpendicular to the longitudinal axis and faces
away from the hub. The upper flange is further includes an interior
surface that forms an angle of substantially 60 degrees with
respect to the longitudinal axis. The lower flange is disposed at
the second end of the hub, and includes an exterior surface that is
substantially perpendicular to the longitudinal axis and facing
away from the hub, and an interior surface forming an angle of
substantially 60 degrees with respect to the longitudinal axis.
[0011] In another embodiment, the upper flange and the lower flange
are fixedly attached to the cylindrical hub.
[0012] In another embodiment, the cylindrical hub, the upper flange
and the lower flange form a unitary component.
[0013] In another embodiment, the unitary component includes a
substantially homogenous material.
[0014] In another embodiment, the upper flange is symmetrically
disposed about the longitudinal axis.
[0015] In another embodiment, the lower flange is symmetrically
disposed about the longitudinal axis.
[0016] In another embodiment, the length of the exterior surface of
the hub, measured from the interior surface of the upper flange to
the interior surface of the lower flange, is substantially equal to
an integral number of diameters of an optical fiber. Thus, an
integer number of turns of that optical fiber will fit at the first
layer, directly against the hub.
[0017] In another embodiment, the composition of the hub, the upper
flange and the lower flange includes a substance having a thermal
expansion characteristic similar to an optical fiber to be wound on
the trapezoidal bobbin. In one embodiment, the substance includes
plastic. In another embodiment, the substance includes a composite
material.
[0018] In another aspect, a trapezoidal optical fiber coil use in a
fiber optic gyroscope comprises a bobbin and a predetermined length
of optical fiber wound about the bobbin in succeeding layers. The
bobbin includes a cylindrical hub characterized by a longitudinal
axis, a first end, a second end and an exterior surface, the hub
being symmetrically disposed about the longitudinal axis. The
bobbin also includes an upper flange symmetrically disposed about
the longitudinal axis at the first end of the hub. The upper flange
is characterized by an exterior surface that is substantially
perpendicular to the longitudinal axis and faces away from the hub.
The upper flange is further characterized by an interior surface
that forms an angle of substantially 60 degrees with respect to the
longitudinal axis. The bobbin further includes a lower flange
symmetrically disposed about the longitudinal axis at the second
end of the hub. The lower flange is characterized by an exterior
surface that is substantially perpendicular to the longitudinal
axis and faces away from the hub. The lower flange is further
characterized by an interior surface that forms an angle of
substantially 60 degrees with respect to the longitudinal axis. A
predetermined length of optical fiber is wound about the bobbin in
succeeding layers extending from the longitudinal axis in a radial
direction. The first layer is disposed upon the exterior surface of
the hub in an integer number of turns of the optical fiber, and
each subsequent layer having an integer number of turns greater
than the next preceding layer.
[0019] In another embodiment, the upper flange and the lower flange
are fixedly attached to the cylindrical hub.
[0020] In another embodiment, the cylindrical hub, the upper flange
and the lower flange form a unitary component.
[0021] In another embodiment, the unitary component includes a
substantially homogenous material.
[0022] In another embodiment, the upper flange is symmetrically
disposed about the longitudinal axis.
[0023] In another embodiment, the lower flange is symmetrically
disposed about the longitudinal axis.
[0024] In another embodiment, a length of the exterior surface of
the hub, measured from the interior surface of the upper flange to
the interior surface of the lower flange, is substantially equal to
an integral number of diameters of an optical fiber.
[0025] In another embodiment, the composition of the hub, the upper
flange and the lower flange includes a substance having a thermal
expansion characteristic similar to an optical fiber to be wound on
the trapezoidal bobbin.
[0026] In another embodiment, the substance includes plastic.
[0027] In another embodiment, the substance includes a composite
material.
[0028] In another embodiment, the optical fiber, viewed in a plane
intersecting the longitudinal axis, is arranged in a quadrupolar
pattern.
[0029] Another embodiment further includes a layer of epoxy
disposed between the first layer of optical fiber and the exterior
surface of the hub.
[0030] Another embodiment further includes a layer of epoxy
disposed between each adjacent layer of optical fiber.
[0031] In another aspect, a trapezoidal bobbin for providing a
foundation about which an optical fiber is wound comprises hub
means, upper flange means and lower flange means. The hub means
provides an elongated form for winding optical fiber, and includes
a longitudinal axis, a first end, a second end and an exterior
surface. The hub is symmetrically disposed about the longitudinal
axis. The upper flange means terminates the first end of the hub,
and includes an exterior surface that is substantially
perpendicular to the longitudinal axis, and faces away from the
hub. The upper flange also includes an interior surface that forms
an angle of substantially 60 degrees with respect to the
longitudinal axis. The lower flange means terminates the second end
of the hub, and includes an exterior surface that is substantially
perpendicular to the longitudinal axis and faces away from the hub.
The lower flange also includes an interior surface forming an angle
of substantially 60 degrees with respect to the longitudinal
axis.
[0032] In another aspect, a method of winding a optical fiber about
a trapezoidal bobbin comprises winding, with a first feed spool and
a second feed spool, the optical fiber about the cylindrical hub of
the bobbin. The cylindrical hub includes a longitudinal axis, a
first end, a second end and an exterior surface. The hub is
symmetrically disposed about the longitudinal axis. The bobbin also
includes an upper flange that is symmetrically disposed about the
longitudinal axis at the first end of the hub. The upper flange
includes an exterior surface that is substantially perpendicular to
the longitudinal axis and facing away from the hub. The upper
flange also includes an interior surface that forms an angle of
substantially 60 degrees with respect to the longitudinal axis. The
bobbin also includes a lower flange symmetrically disposed about
the longitudinal axis at the second end of the hub. The lower
flange is characterized by an exterior surface that is
substantially perpendicular to the longitudinal axis and facing
away from the hub, and an interior surface forming an angle of
substantially 60 degrees with respect to the longitudinal axis. The
method includes winding, via the first feed spool, a first layer of
optical fiber about the hub from the upper flange to the lower
flange, such that the first layer includes a first integer number
of turns of the optical fiber. The method further includes moving
the first feed spool in a direction parallel to the longitudinal
axis to a location away from the first layer of optical fiber. The
method further includes winding, via the second feed spool, a
second layer of optical fiber about the hub overlaying the first
layer of optical fiber, from the upper flange to the lower flange.
The second layer is wound so as to include an integer number of
turns that is equal to one more than the first integer number of
turns. The method also include winding, via the second feed spool,
a third layer of optical fiber about the hub on top of the second
layer of optical fiber, from the lower flange to the upper flange.
The second layer is wound so as to include a third integer number
of turns that is equal to one more than the second integer number
of turns. The method further includes moving the second feed spool
in a direction parallel to the longitudinal axis, to a location
away from the third layer of optical fiber. The method also
includes winding, via the first feed spool, a fourth layer of
optical fiber about the hub on top of the third layer of optical
fiber, from the lower flange to the upper flange. The fourth layer
includes a fourth integer number of turns that is equal to one more
than the third integer number of turns.
[0033] Another embodiment of the invention further includes
repeating, after winding the fourth layer of optical fiber, the
winding of the first, second, third and fourth layers, so as to
apply at least two sets of four layers on the trapezoidal
bobbin.
[0034] Another embodiment of the invention further includes
arranging the layers of optical fiber so as to create a quadrupolar
pattern when the layers are viewed in a plane intersecting the
longitudinal axis.
BRIEF DESCRIPTION OF DRAWINGS
[0035] The foregoing and other objects of this invention, the
various features thereof, as well as the invention itself, may be
more fully understood from the following description, when read
together with the accompanying drawings in which:
[0036] FIG. 1A shows a perspective view of a typical prior art
bobbin;
[0037] FIG. 1B shows a cross-sectional view of the prior art bobbin
of FIG. 1A;
[0038] FIG. 2 shows a stress profile from a finite element model of
the prior art bobbin of FIG. 1A;
[0039] FIG. 3 illustrates one embodiment of a trapezoidal bobbin
for providing a foundation for an optical fiber coil; and,
[0040] FIG. 4 shows a stress profile from a finite element model of
the trapezoidal bobbin of FIG. 3.
[0041] FIG. 5 shows the optical fiber being wound onto the
trapezoidal bobbin of FIG. 3; and,
[0042] FIG. 6 shows the first four layers of the optical fiber on
the trapezoidal bobbin of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] FIG. 3 illustrates one embodiment of a trapezoidal bobbin
100, including an upper flange 102 and a lower flange 104 disposed
at either end of a cylindrical hub 106. In some embodiments, the
hub 106 and flanges 102 and 104 are separate components and the
flanges 102 and 104 are fixedly attached to the hub 106. In other
embodiments, the hub 106 and flanges 102 and 104 form a unitary
component, i.e., the hub and flanges are formed as a single
component, without any type of interface or boundary where the hub
106 ends and the flange (102 or 104) begins. In some embodiments,
the unitary component is made of a material that is homogenous or
nearly homogeneous, i.e., the material properties are the same or
nearly the same throughout the component. In one embodiment, the
trapezoidal bobbin 100 is made of plastic. In other embodiments,
the trapezoidal bobbin 100 is made of a composite material. In
general, the trapezoidal bobbin is made of a material that has a
thermal expansion characteristic similar to that of the optical
fiber that is to be wound on it. The upper flange 102, lower flange
104 and hub 106 are symmetrically disposed about a central axis AX.
The longitudinal dimension 108 of the upper flange 102 and the
lower flange 106 (i.e., the dimension along a line parallel to the
axis AX) decreases with the radial distance from the axis AX. Each
flange is thus thickest (i.e., the longitudinal dimension 108 is
greatest) at the exterior surface 110 of the cylindrical hub 106,
and thinnest (i.e., the longitudinal dimension 108 is smallest) at
the point farthest from the axis AX. In one embodiment, the
longitudinal dimension is non-zero at the point farthest from the
axis, so that the outer edge 126 of the flange is blunt rather than
pointed. In other embodiments, the longitudinal dimension 108 is
zero or near-zero at the point farthest from the axis, so that the
outer edge 126 of the flange is pointed.
[0044] The first (base) layer of optical fiber is wound upon
exterior surface 110 of the cylindrical hub 106. In one embodiment
of the bobbin 100, the angle 120 between the hub 106 and the
interior flange surface 122 is exactly 60 degrees. In other
embodiments, the angle 120 is only approximately 60 degrees. For
example, the angle may be optimally 60 degrees with some allowable
angle error, such as +/-5 degrees, although other angle error
margins may also be used. In yet other embodiments, the angle 120
between the hub and the interior flange surface 120 another angle
suitable to the particular winding pattern used to apply the
optical fiber to the bobbin. Further, the length 124 of the
exterior surface 110, measured from the upper flange 102 to the
lower flange 104, is such that the first layer of optical fiber is
characterized by an integer number of fiber turns. Because of the
60 degree angle between the hub 106 and the interior flange surface
122, the second layer of optical fiber has one additional turn with
respect to the first layer, the third layer of optical fiber has
two additional turn with respect to the first layer, etc. In
general, the N.sup.th layer of optical fiber has N-1 additional
turns with respect to the first (base) layer. The completed fiber
coil is therefore trapezoidal in cross section, as is shown in FIG.
3.
[0045] One advantage of the trapezoidal bobbin 100 shown in FIG. 3
is increased stability, due to the thickness of the flanges 102 and
104, with respect to the flanges of the prior art. The greater
thickness of the flanges 102 and 104 in the longitudinal dimension
108 (with respect to the prior art) increases the frequencies of
the natural modes of vibration of the bobbin 100, resulting in an
extremely stable coil in high shock and vibration environments.
[0046] Another advantage of the trapezoidal bobbin 100 is a
significant reduction in the thermally induced stresses within the
bobbin 100, and consequently also in the optical fiber coil that is
wound on the bobbin 100. This advantage may be observed by
comparing the temperature-induced stresses in a prior art bobbin
assembly (see FIG. 2), to the results of a finite element model
representing an embodiment of a trapezoidal bobbin 100 (see FIG.
4). As was described herein, the optical fiber is typically wound
onto the hub 106 with an epoxy adhesive so that the FOG can operate
in high vibration environments. FIG. 2 plots the predicted stresses
generated in a prior art bobbin, for which the zero stress
temperature is +85 degrees Celsius and the stresses are calculated
at the lowest operating temperature of the coil (-54 degrees
Celsius). Due to the relatively large thermal expansion of the
epoxy adhesive at temperatures below the zero stress temperature,
the bobbin flanges are subjected to bending forces, generating
large stresses in the flange at, and in regions near, the hub
interface 130. Comparing FIG. 2 to FIG. 4, bobbins with the
trapezoidal flange of FIG. 4 demonstrate at least a factor of two
reduction in stress, relative to the prior art bobbin of FIG. 2.
Consequently, the resultant stress on the optical fiber with the
trapezoidal bobbin is generally lower than with a prior art
bobbin.
[0047] The trapezoidal bobbin offers further advantages over the
prior art in the process of winding the optical fiber onto the
bobbin. As described in more detail herein, the optical fiber coil
used in fiber optic gyroscopes is often wound in a quadrupolar
pattern. Because the optical coil on the trapezoidal bobbin 100
increments by exactly one turn per layer (described herein), the
optical fiber wound on the trapezoidal bobbin 100 can "climb" up
the interior flange surface 122 without interfering with
intermediate layers from the alternate feed spool.
[0048] Yet another advantage of the trapezoidal bobbin 100 is that
no slot is required in the flange to allow the fiber from the
non-winding feed spool to exit the active winding area, as was
described herein for the prior art bobbins. Because the trapezoidal
bobbin has flanges that are angled with respect to a plane
perpendicular to the hub, the end of the fiber that is not being
wound (i.e., the inactive end) is simply moved over, away from the
active winding area, to prevent interference with the active guide
wheel. This advantage is illustrated in FIG. 5. The idle fiber 140
from the idle feed spool is shown off to one side while the active
guide wheel 142 applies the active fiber from the active feed spool
to the bobbin. The lack of slots for allowing the fiber from the
feed spools to exit the winding area allows the flanges to maintain
their structural integrity and thus their mechanical stability.
FIG. 6 shows the first four layers of optical fiber on the
trapezoidal bobbin, illustrating that the first feed spool applies
the first layer, the second feed spool applies the second and the
third layers, and the first feed spool applies the fourth layer, as
was described herein in general for prior art bobbins. The first
and second feed spools apply additional sets of four layers onto
the trapezoidal bobbin using the same first-second-second-first
application pattern.
[0049] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The present embodiments are therefore to be considered in
respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description, and all changes which come within the
meaning and range of the equivalency of the claims are therefore
intended to be embraced therein.
* * * * *