U.S. patent application number 10/079102 was filed with the patent office on 2003-01-16 for low cost optomechanical mount for precisely steering/positioning a light beam.
Invention is credited to Wayne, Kenneth J..
Application Number | 20030010873 10/079102 |
Document ID | / |
Family ID | 25423117 |
Filed Date | 2003-01-16 |
United States Patent
Application |
20030010873 |
Kind Code |
A1 |
Wayne, Kenneth J. |
January 16, 2003 |
Low cost optomechanical mount for precisely steering/positioning a
light beam
Abstract
An optomechanical mounting includes an upper set of balls and a
lower set of balls that support and secure a sphere containing an
optical element. The materials in the mounting have the same or
nearly the same coefficient of thermal expansion and the balls
provide opposing radial forces so that thermal expansions are
compensated, giving the mounting superior thermal stability.
Frictional forces on the sphere from the upper and lower set of
balls maintain the orientation of the sphere (and the optical
element) during operation, but smooth surfaces of the sphere and
balls still permit sensitive, precision rotation of sphere for
alignment without post-alignment clamping of the sphere.
Inventors: |
Wayne, Kenneth J.;
(Saratoga, CA) |
Correspondence
Address: |
AGILENT TECHNOLOGIES, INC.
Legal Department, DL429
Intellectual Property Administration
P.O. Box 7599
Loveland
CO
80537-0599
US
|
Family ID: |
25423117 |
Appl. No.: |
10/079102 |
Filed: |
February 19, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10079102 |
Feb 19, 2002 |
|
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09906869 |
Jul 16, 2001 |
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Current U.S.
Class: |
248/64 |
Current CPC
Class: |
G02B 7/1824 20130101;
G02B 7/008 20130101; G02B 7/00 20130101 |
Class at
Publication: |
248/64 |
International
Class: |
F16L 003/00; E21F
017/02 |
Claims
I claim:
1. An optomechanical system comprising: a sphere adapted to receive
an optical element; a first set of curved surfaces in contact with
the sphere; and a second set of curved surfaces in contact with the
sphere, the first and second set of curved surfaces so constructed
and arranged such that the sphere has freedom for prescribed
movement when required, but is otherwise stationary.
2. The system of claim 1, wherein each member of the first set of
curved surfaces contacts the sphere at approximately just one
point, and each member of the second set of curved surfaces
contacts the sphere at approximately just one point.
3. The system of claim 2, wherein each member of the first set of
curved surfaces is a ball, and each member of the second set of
curved surfaces is a ball.
4. The system of claim 3, wherein each ball in the first set of
balls has a corresponding ball in the second set of balls, wherein
each ball in the first set applies a force to the sphere that is
collinear with and opposite to a force that the corresponding ball
in the second set applies to the sphere.
5. The system of claim 4, further comprising a housing adapted to
receive the sphere, first and second set of balls.
6. The system of claim 5, further comprising a lid attached to the
housing to apply a downward force upon the first set of balls,
sphere, and second set of balls.
7. The system of claim 6, wherein the sphere and each ball in the
first and second set of balls are made of steel.
8. The system of claim 6, wherein each ball in the first set
comprises a ceramic ball.
9. The system of claim 8, wherein each ball in the second set
comprises a steel ball.
10. The system of claim 6, wherein each ball in the second set
comprises a ceramic ball.
11. The system of claim 1, wherein the sphere includes an opening
adapted for insertion of a tool for rotating the sphere while the
first and second set of curved surfaces hold the sphere in
position.
12. The system of claim 11, wherein the sphere and the first and
second set of curved surfaces have finishes that permit smooth
rotation of the sphere in response to forces applied via the
alignment tool while the curved surfaces apply forces required for
holding the sphere in alignment during normal use.
13. The system of claim 1, wherein the first set of curved surfaces
comprises three curved surfaces and the second set of curved
surfaces also comprises three curved surfaces.
14. The system of claim 13, wherein the first set of three curved
surfaces comprises 3 balls and the second set of three curved
surfaces also comprises 3 balls.
15. An optomechanical system comprising: a sphere adapted for
mounting an optical element in the sphere, the sphere having an
opening shaped to receive an alignment tool; and a plurality of
magnets in contact with the sphere, the magnets so constructed and
arranged such that the sphere has freedom for prescribed movement
when required, but is otherwise stationary.
16. The system of claim 15, further comprising a housing adapted to
receive the sphere and magnets.
17. The system of claim 16, further comprising a cover attached to
the housing.
18. The system of claim 17, further comprising a spring attached to
the cover for applying a downward force upon the sphere.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 09/906,869 of Kenneth J. Wayne et al, filed on
Jul. 16, 2001, entitled "Optomechanical Mount for Precisely
Steering/Positioning a Light Beam." The disclosure of co-pending
application Ser. No. 09/906,869 is herein incorporated by
reference.
BACKGROUND
[0002] Many optical systems require precision optomechanical
mountings that hold optical elements in the positions and
orientations required for operation of the system. To achieve
proper positioning and alignment of an optical element, an
optomechanical mounting generally must allow movement or rotation
of the optical element relative to other optical elements during an
alignment process, but once the optical element is aligned the
mounting must securely hold the optical element to maintain the
proper alignment during shipping and use of the optical system.
[0003] FIG. 1 shows a prior art optomechanical mount 101, as
disclosed in application Ser. No. 09/906869. A sphere 105 is
sandwiched between a lower spring assembly 107 and an upper spring
assembly 109. The sphere 105 contains an optical element (not
shown) and has openings 110 for light paths to pass through. The
sphere 105 also has openings 111 that fit an alignment tool used to
rotate the sphere 105 during alignment. When a cover (not shown) is
clamped down over the sphere 105 and spring assemblies 107 and 109,
springs (not shown) in the spring assemblies 107 and 109 apply
force to keep the sphere 105 in place after alignment.
[0004] The optomechanical mount 101 exhibits excellent long-term
alignment stability when subjected to temperature changes, shock,
and vibration. However, the optomechanical mount 101 is relatively
expensive to manufacture. The spring assemblies 107 and 109, in
particular, have many complex parts, making the optomechanical
mount 101 difficult and time-consuming to build. Therefore, it is
desirable to have an optomechanical mount that maintains precise
angular orientation of the optical element without requiring as
many parts or as much assembly time as the optomechanical mount
101.
SUMMARY
[0005] In accordance with a preferred aspect of the invention,
rigid balls are used to support and apply force to a sphere
containing an optical element fixed at its center. A lower set of
balls supports the sphere, and an upper set of balls rests on top
of the sphere. Generally, each ball in the lower set has a
corresponding ball in the upper set; each ball in the lower set
applies a force to the sphere that is collinear with and opposite
to a force that the corresponding ball in the upper set applies to
the sphere. All ball forces are directed through the center of the
sphere. As used herein, the "center" of the sphere refers to the
true center of the sphere, not the center of mass. The opposing
forces from the balls maintain positional stability of the sphere
when the optomechanical mounting is subjected to thermal
variations, vibrations, or shock. The balls and other components
should be made of the same material or materials having
substantially similar coefficients of thermal expansion (CTEs), so
that thermal expansion of the assembly and component parts does not
result in a rotation of the sphere containing the optical element.
This gives the optomechanical mounting superior thermal
stability.
[0006] The sphere and balls are enclosed within a housing and held
in place by a lid. The housing preferably has cavities recessed in
its base to hold the lower set of balls. The housing has openings
in the center for light paths of the optical element or for access
to the sphere during the alignment process. The sphere and upper
set of balls are aligned in the housing on top of the lower set of
balls before the lid is attached to the housing. The lid aligns the
upper set of balls and applies force, such that each ball in the
upper set applies a force to the sphere that is collinear and
diametrically opposed to a force from a ball in the lower set.
These forces are strong enough to hold the sphere in position and
to resist alignment changes due to mechanical shocks once the
optomechanical mount is completely assembled. At the same time, the
fine surface finishes on the sphere and the balls allow the sphere
to be rotated smoothly, and with high resolution, once surface
friction between the sphere and the balls is overcome.
[0007] In another embodiment, the sphere can be held in place by
high-strength magnets. The magnetic force is sufficient to hold the
sphere in alignment, yet weak enough to be overcome when the sphere
is rotated with an alignment tool.
[0008] These embodiments require fewer parts and less assembly time
than the prior art optomechanical mount 101. Therefore, the cost of
manufacturing for the present invention is lower.
DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a perspective view of a prior art optomechanical
mounting, as disclosed in application Ser. No. 09/906,869.
[0010] FIG. 2A is a perspective view of an optomechanical mounting
in accordance with an embodiment of the invention.
[0011] FIG. 2B is a perspective view of an optomechanical mounting
in accordance with an embodiment of the invention, with the housing
removed to show inside detail.
[0012] FIG. 2C is a perspective view of the housing of an
optomechanical mounting in accordance with an embodiment of the
invention.
[0013] FIGS. 3A and 3B show alternate structures that can be used
in place of balls to constrain the sphere.
[0014] FIG. 4A shows an alternate embodiment of the present
invention.
[0015] FIG. 4B shows a means for applying downward force upon an
alternate embodiment of the present invention.
[0016] Use of the same reference symbols in different figures
indicates similar or identical items.
DETAILED DESCRIPTION
[0017] In accordance with an aspect of the invention, a lower and
an upper set of rigid balls supports a sphere containing an optical
element. The balls are substantially identical and are oriented so
that each ball applies a force along a radius of the sphere. Each
of these forces is collinear with an opposing force from a ball
from the other set of balls. The balls accordingly hold the sphere
in position with a high degree of thermal stability because the
housing, sphere, and support balls are made of materials having
identical or substantially similar CTEs. Therefore, the housing,
sphere, and support balls all expand and contract in unison without
imparting rotation to the sphere containing the optical
element.
[0018] FIG. 2A is a perspective view of an optomechanical assembly
201 in accordance with an embodiment of the present invention. A
sphere 105 rests on support balls 207 in a housing 203. The sphere
105 is adapted to receive an optical element (not shown). Upper
balls 209 are arranged on the sphere 105 and partially constrained
by the sphere 105 and the central bore of the housing 203. A lid
211 is attached to the housing 203. The lid 211 has openings 212
that fit over the upper balls 209. Each ball in the support balls
207 has a corresponding ball in the upper balls 209. Each pair of
balls is diametrically opposed from its matching mate, so that the
forces exerted by each pair on the sphere 105 are equal and
opposite in direction.
[0019] The housing 203 has openings 205 for light paths to and from
the sphere 105, or to allow access to the sphere 105 during the
alignment process. The housing 203 is preferably made out of the
same rigid material as the balls, such as steel. Since the housing
203 has flat surfaces and is cubic in shape, it is less costly to
machine and manufacture than the rounded spring assemblies 107 and
109 shown in the prior art of FIG. 1.
[0020] FIG. 2B is a perspective view of the optomechanical assembly
201 shown in FIG. 2A, with the housing 203 removed so as to better
illustrate the arrangement of the sphere 105, the support balls
207, the upper balls 209, and the lid 211. In the exemplary
embodiment, the support balls 207 are placed so that when the upper
balls 209 are in position, each one of the support balls 207 is
diametrically opposed to a corresponding ball in the set of upper
balls 209. In this fashion, equal and opposite forces are applied
to the sphere 105. For example, the balls 207-1, 207-2, and 207-3
can be located at 0.degree., 120.degree., and 240.degree. in a
plane normal to a vertical axis of sphere 105, while the balls
209-1, 209-2, and 209-3 are located at 180.degree., 300.degree.,
and 60.degree. around another plane normal to the vertical axis.
With this configuration, force vectors for a pair of balls (207-1,
209-1), (207-2, 209-2), or (207-3, 209-3) are collinear and pass
through the center of the sphere 105. Each support ball 207 thus
has a corresponding upper ball 209 that provides an equal,
collinear opposing force through the center of the sphere 105.
Accordingly, balls 207 and 209 do not apply a torque to the sphere
105, and changes in the upper balls 209, for example, caused by
changes in temperature, counter or cancel corresponding changes in
the support balls 207 to keep the sphere 105 from shifting
position.
[0021] The illustrated embodiment depicts three balls in the
support balls 207 and three balls in the upper balls 209 for a
total of six balls. This is a preferred number of balls, since the
sphere 105 is minimally constrained. However, more balls can be
used. The support balls 207 and the upper balls 209 are identical
in size and shape. In a working embodiment of the invention, the
balls used were approximately 11.1 mm in diameter. The balls can be
varied in size without affecting the functionality of the
invention. The balls precisely position the sphere 105 so that the
center of the sphere 105 remains in place during and after
alignment.
[0022] The sphere 105 contains an optical element (not shown) such
as a mirror, a beam splitter, a translating window, a wedge window,
or a lens. Optical elements mounted in the sphere 105 can vary
widely, but generally, the center of the sphere 105 lies on the
optical center, which may be an optical surface, an axis, and/or a
symmetry plane of the optical element in the sphere 105. In the
exemplary embodiment, the sphere 105 is a precision bearing about
41.275 mm in diameter that is machined to include openings 110 for
light paths to and from the optical element. The sphere 105 can
further include openings 112 that fit an alignment tool such as an
Allen key or lever that can be used to rotate the sphere 105 in the
finished optomechanical assembly 201. Additional access ports for
tooling can be provided at almost any position, notably at
45.degree. positions in a vertical plane. The sphere 105 can be
rotated about any axis running through its center. The forces
exerted by the support balls 207 and upper balls 209 hold the
sphere 105 in place and protect it from shocks or jars that might
disturb the alignment of the sphere 105.
[0023] The lid 211 has openings 212, one for each of the upper
balls 209. The openings 212 are narrower than the diameter of the
upper balls 209, so that the edges of the openings 212 will contact
the surfaces of the upper balls 209 when the lid 211 is placed over
the upper balls 209. When the lid 211 is attached to the housing
203, the contact points transfer the downward force from the lid
211 to the upper balls 209, and keep the upper balls 209 in
position. The lid 211 also has a central opening 210, to allow a
light path or an alignment tool to access the sphere 105.
[0024] All of the components in the optomechanical assembly 201 can
be made of the same material or materials that are substantially
the same or at least have the same or similar CTEs. If the CTEs are
the same, the entire assembly expands or contracts in unison when
subjected to a temperature change. Thus, the sphere 105 will not
rotate during acclimatization, and the angular alignment of the
optical element is preserved when the temperature changes. In an
actual working embodiment, stainless steel was used to make the
housing 203, support balls 207, upper balls 209, sphere 105, and
lid 211. However, other rigid materials, such as steel, Invar, etc.
can also be used.
[0025] The sphere 105, support balls 207, and upper balls 209
should have surface finishes that permit rotation of the sphere
during alignment. If the sphere 105, support balls 207, and upper
balls 209 are all made of the same material, then it is possible
that galling (microscopic cold welding) will occur between the
sphere 105 and the other balls as the sphere 105 is rotated during
adjustment. If the system will only be adjusted a few times, this
is not a serious problem and indeed may even be an advantage
because the long-term stability of the setting is improved.
However, if the system will be adjusted frequently, it is
preferable to reduce the surface friction between the sphere 105,
support balls 207, and upper balls 209 so as to prevent
galling.
[0026] One method of reducing surface friction, if cleanliness is
not a requirement, is to lubricate the components of optomechanical
assembly 201. If cleanliness is a consideration, another option is
to make support balls 207, or upper balls 209, or both sets of
balls out of a material that has less surface frictional force to
overcome. A ceramic such as silicon nitride is one possible
material. If the primary concern is reduced surface friction and
smooth adjustment for the sphere 105, a copper alloy such as brass
or bronze may also be used. However, using a copper alloy may
negatively impact thermal stability, durability, and shock
stability.
[0027] FIG. 2C is a perspective view of just the housing 203. The
housing 203 has depressions 213 in its base. The support balls 207
(not shown) fit into the depressions 213, and are secured with
epoxy, welding, press fitting, screws, or any other method of
attachment. The housing 203 has a hole 215 in its base to allow
access to the sphere 105 for a light path or an alignment tool.
[0028] To assemble the optomechanical assembly 201, the support
balls 207 are set into the depressions 213 of the housing 203 and
fixed in place. The sphere 105 is placed onto the support balls
207, and then the upper balls 209 are arranged around the sphere
105 as previously described. The upper balls 209 stand slightly
above the top face of housing 203. Finally, the lid 211 is screwed
onto housing 203 or otherwise secured over the upper balls 209. The
lid 211 applies a downward spring force to each one of the upper
balls 209. The magnitude of this force is fixed by the height of
the ball contact points above the top face of the housing 203, the
stiffness of the lid 211, and fabrication tolerances. The selection
of this magnitude will depend on the shock/vibration environment.
In an actual working embodiment, the force was approximately 15 to
20 pounds per upper ball 209.
[0029] The sphere 105 may be constrained using structures other
than support balls 207 and upper balls 209. For instance,
hemispheres and smaller portions of spheres can be used in the
place of balls. FIG. 3A shows some possible substitute structures
for support balls 207 and upper balls 209. The best structures have
surfaces that will contact the sphere 105 at approximately a single
point. The examples shown in FIG. 3A have spherical surface
portions that will contact the sphere 105 at approximately a single
point. The word "approximately" is used because it is almost
impossible to manufacture such perfect surfaces that will contact
and remain in contact with each other at exactly a single
point.
[0030] Other structures may be used that have many points of
contact with the sphere 105. FIG. 3B illustrates one such example.
However, these structures generate higher frictional forces and
make alignment of the sphere 105 difficult. There are other
well-known methods for supporting the sphere 105 that will maintain
rotational freedom about any axis. For instance, using a conical
surface to support a sphere is a method well known in the art.
[0031] FIG. 4A shows an alternate embodiment of the present
invention, using high-strength magnets 401 to hold the sphere 105
in place. The magnets 401 can be fixed to the base of the housing
203 (not shown) with any well-known means such as epoxy, press
fitting, etc. Some possible high-strength magnets are alnico,
ceramic, and rare-earth magnets. The magnets 401 are mounted so
that they are slightly angled in towards the sphere 105, to
facilitate contact with the surface of the sphere 105. Due to the
perspective of FIG. 4A, only two magnets 401 can be seen; a third
magnet 401 is positioned out of sight behind the sphere 105, such
that all three magnets 401 are positioned at equidistant intervals
around the sphere 105. Although only three magnets 401 are shown in
the figure, more than three magnets can be used.
[0032] The magnets 401, as drawn, are rectangular in shape, but can
also be circular or any other shape. Obviously, the sphere 105
should be made of a material that will be attracted to the magnets
401. The sphere 105 is placed upon the magnets 401, and the
magnetic force holds the sphere 105 in place when the sphere 105 is
not being aligned. The magnets should be chosen so that their
magnetic force is strong enough to keep the sphere 105 in
alignment, yet weak enough to be overcome when the sphere 105 is
rotated with an alignment tool. No upper magnets are needed in
contact with the sphere 105, since any upper magnets would tend to
pull the sphere 105 away from the magnets 401.
[0033] If the magnets 401 do not have enough magnetic pull on the
sphere 105, it may be necessary to apply a downward force upon the
sphere 105 to prevent it from lifting off of the magnets 401 during
the alignment process. FIG. 4B shows one possible means for
applying a downward force 403 upon the sphere 105. A cover 405 for
the housing 203 (not shown) has a contact 407 mounted on a spring
309. When the cover 405 is attached to the housing 203, the contact
407 pushes against the surface of the sphere 105. The spring 309
provides the downward force 403 to keep the sphere 105 from lifting
off of the magnets 401 while it is being aligned.
[0034] Although the invention has been described with reference to
particular embodiments, the described embodiments are only examples
of the invention's application and should not be taken as
limitations. For example, although specific dimensions and
materials were described for an exemplary embodiment of the
invention, those dimensions and materials are subject to wide
variations and replacements. Various other adaptations and
combinations of features of the embodiments disclosed are within
the scope of the invention as defined by the following claims.
* * * * *