U.S. patent application number 11/046252 was filed with the patent office on 2006-08-03 for passively aligned optical elements.
Invention is credited to Scott C. Cahall, Carl F. Leidig, Paul D. Ludington, Joseph M. Recco, James A. Schmieder.
Application Number | 20060171046 11/046252 |
Document ID | / |
Family ID | 36190695 |
Filed Date | 2006-08-03 |
United States Patent
Application |
20060171046 |
Kind Code |
A1 |
Recco; Joseph M. ; et
al. |
August 3, 2006 |
PASSIVELY ALIGNED OPTICAL ELEMENTS
Abstract
An optical system has a first lens element (L1) having an outer
portion (36) and a first tapered surface (34). A second lens
element (L2) has an outer portion (26) and a second tapered surface
(24). The first lens element (L1) and the second lens element (L2)
are spaced apart relative to each other and centered relative to
the optical axis (O) by a portion of the first tapered surface (34)
being in contact with a portion of the second tapered surface (24),
the outer portion (36) of the first lens element (L1) being spaced
apart from the outer portion (26) of the second lens element
(L2).
Inventors: |
Recco; Joseph M.;
(Spencerport, NY) ; Schmieder; James A.; (Wayland,
NY) ; Ludington; Paul D.; (Brockport, NY) ;
Cahall; Scott C.; (Fairport, NY) ; Leidig; Carl
F.; (Rochester, NY) |
Correspondence
Address: |
Mark G. Bocchetti;Patent Legal Staff
Eastman Kodak Company
343 State Street
Rochester
NY
14650-2201
US
|
Family ID: |
36190695 |
Appl. No.: |
11/046252 |
Filed: |
January 28, 2005 |
Current U.S.
Class: |
359/811 |
Current CPC
Class: |
G02B 7/022 20130101;
G02B 13/0035 20130101; G02B 7/021 20130101; G02B 27/62
20130101 |
Class at
Publication: |
359/811 |
International
Class: |
G02B 7/02 20060101
G02B007/02 |
Claims
1. An optical system comprising: a first lens element having an
outer portion and a first tapered surface; and a second lens
element having an outer portion and a second tapered surface,
wherein the first lens element and the second lens element are
spaced apart relative to each other and centered relative to an
optical axis by a portion of the first tapered surface being in
contact with a portion of the second tapered surface, the outer
portion of the first lens element being spaced apart from the outer
portion of the second lens element, the first lens element and the
second lens element being positioned adjacent to each other as
viewed alone the optical axis.
2. The optical system of claim 1, the first lens element having an
outer edge portion and the second lens element having an outer edge
portion, wherein the outer edge portion of the first lens element
is contactable with the outer edge portion of the second lens
element while the outer portion of the first lens element remains
spaced apart from the outer portion of the second lens element.
3. The optical system of claim 1, wherein the first tapered surface
is symmetric about the optical axis.
4. The optical system of claim 1, wherein the first tapered surface
has an angle of between 15 and 45 degrees relative to the optical
axis.
5. The optical system of claim 1, the first lens element having a
clear aperture, wherein the clear aperture of the first lens
element is substantially axisymmetric.
6. The optical system of claim 1, the first lens element having a
clear aperture, wherein the clear aperture of the first lens
element is non-axisymmetric.
7. The optical system of claim 1 further comprising: a compliant
spacing member disposed between the outer portion of the first lens
element and the outer portion of the second lens element.
8. The optical system of claim 1, wherein at least one of the first
lens element and the second lens elements is plastic.
9. The optical system of claim 1 further comprising: a lens
mounting structure having an inner surface, wherein one of the
first lens element and the second lens element is not in contact
with the inner surface of the lens mounting structure.
10. The optical system of claim 1, the first lens element having a
clear aperture and the second lens element having a clear aperture,
wherein the first tapered surface is located between the clear
aperture of the first lens element and the outer portion of the
first lens element and the second tapered surface is located
between the clear aperture of the second lens element and the outer
portion of the second lens element.
11. An optical system comprising: a first lens element having an
outer portion and a first tapered surface; a second lens element
having an outer portion and a second tapered surface and a third
tapered surface; and a third lens element having a fourth tapered
surface, wherein the second tapered surface of the second lens
element contacts the first tapered surface of the first lens
element, the third tapered surface of the second lens element
contacts the fourth tapered surface of the third lens element, and
the outer portion of the first lens element is spaced apart from
the outer portion of the second lens element.
12. The optical system of claim 11, the outer portion of the second
lens element being a first outer portion, the second lens element
having a second outer portion, the third lens element having an
outer portion, wherein the second outer portion of the second lens
element is spaced apart from the outer portion of the third lens
element.
13. The optical system of claim 11 further comprising: a lens
mounting structure having an inner surface, wherein at least one of
the first lens element, the second lens element, and the third lens
element is not in contact with the inner surface of the lens
mounting structure.
14. A method of manufacturing an optical system comprising:
providing a first lens element having an outer portion and a first
tapered surface; providing a second lens element having an outer
portion and a second tapered surface; and positioning the first
lens element and the second lens element relative to each other by
contacting a portion of the first tapered surface with a portion of
the second tapered surface with the outer portion of the first lens
element being spaced apart from the outer portion of the second
lens element, wherein positioning the first lens element and the
second lens element includes positioning the first lens element and
the second lens element adjacent to each other as viewed along an
optical axis.
15. The method of claim 14 further comprising: providing a mounting
structure; applying a force against the outer portion of at least
one of the first and second lens elements; and fixing the first and
second lens elements relative to the mounting structure.
16. The method of claim 15, wherein fixing the first and second
lens elements relative to the mounting structure comprises applying
an adhesive to at least one of the first and second lens elements
and the mounting structure.
17. The method of claim 15, wherein fixing the first and second
lens elements relative to the mounting structure comprises applying
a weld to at least one of the first and second lens elements and
the mounting structure.
18. The method of claim 15, wherein fixing the first and second
lens elements relative to the mounting structure comprises
providing a retaining ring to within the mounting structure.
19. The method of claim 14 further comprising: positioning a
compliant spacer between the outer portion of the first lens
element and the outer portion of the second lens element.
20. The optical system of claim 1 further comprising: a compliant
spacing member disposed between the first lens element and the
second lens element.
21. An optical system comprising: a first lens element having a
first tapered surface; a second lens element having a second
tapered surface; and a third lens element having a third tapered
surface, the third lens element being spaced apart from the second
lens element, wherein the second tapered surface of the second lens
element contacts the first tapered surface of the first lens
element, and the third tapered surface of the third lens element
contacts the first tapered surface of the first lens element.
22. The optical system of claim 1, wherein the first tapered
surface has an angle of between 5 and 70 degrees relative to the
optical axis.
23. An optical system comprising: a first lens element having an
outer portion, an outer edge portion, and a first tapered surface;
and a second lens element having an outer portion, an outer edge
portion, and a second tapered surface, the first lens element and
the second lens element being spaced apart relative to each other
and centered relative to an optical axis by a portion of the first
tapered surface being in contact with a portion of the second
tapered surface, the outer portion of the first lens element being
spaced apart from the outer portion of the second lens element,
wherein the outer edge portion of the first lens element is
contactable with the outer edge portion of the second lens element
while the outer portion of the first lens element remains spaced
apart from the outer portion of the second lens element.
24. An optical system comprising: a first lens element having an
outer portion and a first tapered surface; a second lens element
having an outer portion and a second tapered surface; and a
compliant spacing member disposed between the outer portion of the
first lens element and the outer portion of the second lens
element, wherein the first lens element and the second lens element
are spaced apart relative to each other and centered relative to an
optical axis by a portion of the first tapered surface being in
contact with a portion of the second tapered surface, the outer
portion of the first lens element being spaced apart from the outer
portion of the second lens element.
25. The optical system of claim 24 further comprising: a lens
mounting structure having an inner surface, wherein one of the
first lens element and the second lens element is not in contact
with the inner surface of the lens mounting structure.
26. The optical system of claim 24, wherein the first tapered
surface has an angle of between 5 and 70 degrees relative to the
optical axis.
27. An optical system comprising: a first lens element having an
outer portion and a first tapered surface; a second lens element
having an outer portion and a second tapered surface; and a lens
mounting structure having an inner surface, wherein one of the
first lens element and the second lens element is not in contact
with the inner surface of the lens mounting structure, and the
first lens element and the second lens element are spaced apart
relative to each other and centered relative to an optical axis by
a portion of the first tapered surface being in contact with a
portion of the second tapered surface, the outer portion of the
first lens element being spaced apart from the outer portion of the
second lens element.
28. The optical system of claim 27 further comprising: a compliant
spacing member disposed between the outer portion of the first lens
element and the outer portion of the second lens element.
29. The optical system of claim 27, wherein the first tapered
surface has an angle of between 5 and 70 degrees relative to the
optical axis.
30. An optical system comprising: a first lens element having an
outer portion and a first tapered surface; and a second lens
element having an outer portion and a second tapered surface,
wherein the first lens element and the second lens element are
spaced apart relative to each other and centered relative to an
optical axis by a portion of the first tapered surface being in
contact with a portion of the second tapered surface, the outer
portion of the first lens element being spaced apart from the outer
portion of the second lens element, and the first tapered surface
has an angle of between 15 and 45 degrees relative to the optical
axis.
31. An optical system comprising: a first lens element having an
outer portion, a first tapered surface, and a clear aperture; and a
second lens element having an outer portion and a second tapered
surface, wherein the first lens element and the second lens element
are spaced apart relative to each other and centered relative to an
optical axis by a portion of the first tapered surface being in
contact with a portion of the second tapered surface, the outer
portion of the first lens element being spaced apart from the outer
portion of the second lens element, and the clear aperture of the
first lens element is non-axisymmetric.
32. A method of manufacturing an optical system comprising:
providing a first lens element having an outer portion and a first
tapered surface; providing a second lens element having an outer
portion and a second tapered surface; positioning the first lens
element and the second lens element relative to each other by
contacting a portion of the first tapered surface with a portion of
the second tapered surface with the outer portion of the first lens
element being spaced apart from the outer portion of the second
lens element providing a mounting structure; applying a force
against the outer portion of at least one of the first and second
lens elements; and fixing the first and second lens elements
relative to the mounting structure, wherein fixing the first and
second lens elements relative to the mounting structure comprises
applying at least one of a weld and an adhesive to at least one of
the first and second lens elements and the mounting structure.
33. A method of manufacturing an optical system comprising:
providing a first lens element having an outer portion and a first
tapered surface; providing a second lens element having an outer
portion and a second tapered surface; positioning a compliant
spacer between the outer portion of the first lens element and the
outer portion of the second lens element; and positioning the first
lens element and the second lens element relative to each other by
contacting a portion of the first tapered surface with a portion of
the second tapered surface with the outer portion of the first lens
element being spaced apart from the outer portion of the second
lens element.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to optical component
mounting and more particularly relates to an optical apparatus and
method using tapered surfaces to effect alignment of lens
elements.
BACKGROUND OF THE INVENTION
[0002] The growth of portable, personal electronics devices such as
cell phones, PDAs, and similar devices, has spurred development of
miniaturized cameras and light-sensing components that can be
incorporated into these devices. The continuing demand for smaller
and more powerful imaging apparatus, coupled with the requirement
for low cost, presents a considerable challenge to optical and
mechanical design. Low-cost lens assemblies, typically including a
number of plastic lens elements, are being used increasingly for
these applications.
[0003] Although very small plastic lenses can be fabricated
inexpensively at high volumes, the handling, alignment, and
mounting of these tiny optical components into a lens assembly
using multiple components poses significant problems. For mobile
imaging applications, for example, two lens elements should be
laterally aligned (that is, aligned in the plane normal to the
optical axis, where z is the optical axis) to within better than
+/-20 microns. There are also tight tolerances with respect to the
air space, or longitudinal separation along the optical axis (z
axis) between lens elements. Tilt in the two orthogonal directions
.theta..sub.x and .theta..sub.y should be controlled to within tens
of arc-minutes. Clearly, there is considerable challenge in
achieving alignment tolerances in these ranges at low cost when
assembling miniature optical components using mass-produced plastic
lens elements. Conventional active alignment techniques, such as
using point-source microscopy to align centers of curvature
individually, prove too complex and costly for high-volume
production.
[0004] A number of other conventional approaches have been applied
to the problem of lens mounting, alignment and centration of
lenses, including the use of features formed within a lens barrel
or other supporting structure, as described, for example, in U.S.
Pat. No. 6,338,819 entitled "High Numerical Aperture Objective Lens
Assembly" to Leidig and U.S. Pat. No. 4,488,776 entitled "Plastic
Lens Cell" to Skinner. Still other approaches use separate spacing
elements to provide proper alignment and air space between optical
components. For example, referring to FIG. 1, there is shown a lens
mount assembly 10 for mounting multiple lens elements L1, L2, L3
along an optical axis O of a barrel 16. Spacers 12 and surface sags
provide proper air space between lens elements L1, L2, and L3 along
that optical axis. A retaining ring 13 is then used to hold lens
elements L1, L2, and L3 and spacers 12 in place following assembly.
Spacers 12, in conjunction with lens flanges, also provide tilt
alignment .theta..sub.x and .theta..sub.y. Lateral alignment of
lens elements L1, L2, and L3 is accomplished by care in
fabrication, controlling tolerance runout of the lenses, the
outside diameter of the lenses, and the inside diameter of barrel
16 or other optical mounting structure. However, such approaches
increase the overall parts count and assembly complexity and
introduce tolerance build-up that can make proper lens alignment
difficult, particularly as lens assemblies grow smaller.
[0005] Another approach that has been adopted for miniaturized
optical systems uses passive component alignment of lens elements
to each other, rather than to a barrel or to some other enclosure.
Representative examples of optical apparatus using this technique
for centration and spacing include: [0006] U.S. Patent Application
Publication No. 2003/0184885 entitled "Producing Method of Image
Pickup Device" by Tansho et al. discloses an optical unit in which
lens elements are stacked against each other to provide centration,
with additional spacing elements; [0007] U.S. Patent Application
Publication No. 2003/0193605 entitled "Image-Capturing Lens,
Image-Capturing Device and Image Capturing Unit" by Yamaguchi
discloses a lens barrel wherein a flange is provided on each of one
or more stacked lenses, seated against each other to provide both
centration and spacing; [0008] U.S. Pat. No. 4,957,341 entitled
"Integral Type Lens" to Hasegawa discloses a compound projection
lens in which separate lens elements are aligned against each other
using a circumferential flange and guide arrangement; [0009] U.S.
Pat. No. 4,662,717 entitled "Lens and Lens Holding Devices" to
Yamada et al. discloses use of a snap fit for alignment and spacing
of adjacent lenses in a lens holding device; and, [0010] U.S. Pat.
No. 6,072,634 entitled "Compact Digital Camera Objective with
Interdigitated Element Alignment, Stray Light Suppression, and
Anti-Aliasing Features" to Broome et al. discloses passive
alignment between lens elements in which a tapered fit provides
centration and an abutment fit provides proper spacing.
[0011] While each of the above-cited solutions for passive
alignment provide some measure of accuracy for centration and
spacing, there are inherent problems with each of these approaches
that limit their successful application for miniaturized lens
assemblies. In particular, each of these proposed solutions
exhibits problems due to either or both additive tolerance errors
and mechanical overconstraint. The apparatus of both '3605
Yamaguchi and '4885 Tansho et al. disclosures would be particularly
prone to lateral centration problems, requiring precision
fabrication and assembly of the multiple stacked lens components.
For production optical components, in practice, there must
necessarily be some finite gap between a lens element and the
element that provides its lateral constraint, whether this is
provided by a lens barrel or by a structure on an adjacent lens
element. Thus, there is some built-in amount of imprecision that is
inherent to lateral positioning when using conventional lens
mounting techniques as shown in both '3605 Yamaguchi and '4885
Tansho et al. disclosures. The apparatus of both '341 Hasegawa and
'717 Yamada et al. patents exhibit overconstraint, limiting the
applicability of these approaches to lens assemblies. The apparatus
of the '634 Broome et al. patent exhibits both lateral centration
and overconstraint problems, with a tapered centration fit of a
lens element potentially compromised by an abutment fit for spacing
of that same lens element. The '634 Broome et al. solution would
thus require highly accurate manufacturing tolerances in order to
provide suitable centration alignment and spacing. While the high
cost of providing such precision tolerance lens components may be
justified for larger, complex optical assemblies, such a design
approach would not be compatible with requirements for fabrication
of high-volume, low-cost, miniaturized optical assemblies.
SUMMARY OF THE INVENTION
[0012] According to one aspect of the present invention, an optical
system comprises a first lens element having an outer portion and a
first tapered surface; and a second lens element having an outer
portion and a second tapered surface, wherein the first lens
element and the second lens element are spaced apart relative to
each other and centered relative to the optical axis by a portion
of the first tapered surface being in contact with a portion of the
second tapered surface, the outer portion of the first lens element
being spaced apart from the outer portion of the second lens
element.
[0013] According to another aspect of the present invention, an
optical system comprises a first lens element having an outer
portion and a first tapered surface; a second lens element having
an outer portion and a second tapered surface and a third tapered
surface; and a third lens element having a fourth tapered surface,
wherein the second tapered surface of the second lens element
contacts the first tapered surface of the first lens element, the
third tapered surface of the second lens element contacts the
fourth tapered surface of the third lens element, and the outer
portion of the first lens element is spaced apart from the outer
portion of the second lens element.
[0014] According to another aspect of the present invention, an
optical system comprises a first lens element having a first
tapered surface; a second lens element having a second tapered
surface; and a third lens element having a third tapered surface,
the third lens element being spaced apart from the second lens
element, wherein the second tapered surface of the second lens
element contacts the first tapered surface of the first lens
element, and the third tapered surface of the third lens element
contacts the first tapered surface of the first lens element.
[0015] According to another aspect of the present invention, a
method of manufacturing an optical system comprises providing a
first lens element having an outer portion and a first tapered
surface; providing a second lens element having an outer portion
and a second tapered surface; and positioning the first lens
element and the second lens element relative to each other by
contacting a portion of the first tapered surface with a portion of
the second tapered surface with the outer portion of the first lens
element being spaced apart from the outer portion of the second
lens element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In the detailed description of the preferred embodiments of
the invention presented below, reference is made to the
accompanying drawings, in which:
[0017] FIG. 1 is a cross-sectional side view of a lens assembly
showing one conventional centration alignment and spacing
technique;
[0018] FIG. 2 is a cross-sectional side view showing a lens
assembly configured wherein adjacent lenses have a tapered fit,
using the method of the present invention;
[0019] FIG. 3 is a side view showing two lenses adapted for a
tapered fit;
[0020] FIG. 4 is a perspective side view showing the lenses of FIG.
3 from a slight angle;
[0021] FIG. 5 is a perspective view with the lenses of FIG. 3 at
angles that show tapered features;
[0022] FIG. 6 is a schematic side view showing the tapered fit in
an assembly process according to one embodiment;
[0023] FIG. 7A is an enlarged side view showing a spacing element
used in a lens assembly according to one embodiment;
[0024] FIG. 7B is an enlarged side view showing a spacing element
used in a lens assembly according to an alternate embodiment;
[0025] FIG. 8 is a cross-sectional side view showing a lens
assembly having multiple lens elements that are optically aligned
using tapered surfaces;
[0026] FIG. 9 is a cross-sectional side view showing a lens
assembly wherein one lens element has a tapered surface that fits
over the tapered surface of another lens element; and,
[0027] FIG. 10 is a cross-sectional side view showing a lens
assembly wherein multiple lens elements are optically aligned using
tapered surface fittings.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The present description will be directed in particular to
elements forming part of, or cooperating more directly with,
apparatus in accordance with the present invention. It is to be
understood that elements not specifically shown or described may
take various forms well known to those skilled in the art.
[0029] The apparatus and method of the present invention provide a
passive alignment of two lens elements by employing a tapered fit
between the two lens elements. Unlike earlier solutions that use
combinations of tapered and abutment fittings for lens positioning
and alignment, the approach of the present invention uses only a
tapered surface fitting for both lens centration with respect to
the optical axis and lens spacing along the optical axis.
[0030] Referring to FIG. 2, there is shown an optical system 20
according to one embodiment of the present invention. Here, lens
elements L1 and L2 are fitted together within a lens barrel 22 or
other mounting structure, using the tapered fit passive alignment
technique of the present invention. Lateral alignment for lens
components within optical system 20 is provided by lens elements L1
and L3. Lateral alignment for lens element L1 is given by the fit
between the outer diameter (OD) of lens L1, shown as 21 in FIG. 2,
and an inner surface 19 of lens barrel 22. Similarly, lateral
alignment for lens element L3 is given by the fit between the outer
diameter (OD) of lens L3, shown as 18 in FIG. 2, and inner surface
19 of barrel 22. Significantly, lens element L2, with outer
diameter shown as 17 in FIG. 2, does not come into contact with
inner surface 19; instead, outer diameter 17 of lens L2 "floats" in
space with respect to inner surface 19 and does not affect the
lateral alignment of optical assembly 20. Advantageously, lens L2
can have relaxed fabrication tolerances for its outer diameter 17,
as long as there is no contact with inner surface 19 of barrel
22.
[0031] FIGS. 3, 4, and 5 show, in side and perspective views, how
lens elements L1 and L2 are constructed in order to provide a
tapered fit. FIG. 3 shows, in exploded view form, how lens elements
L1 and L2 align with optical axis O. Lens element L2 has a tapered
surface 24, protruding, with a generally convex shape, outward from
the main body of the lens and tapered in a direction toward optical
axis O at an angle A with respect to axis O. Tapered surface 24
lies between a clear aperture 23 for refracting incident light and
an outer portion 26 that lies outside clear aperture 23 and extends
radially outward relative to optical axis O. Lens element L1 has a
generally concave-shaped tapered surface 34 with a taper that
extends in a direction away from optical axis O and that is
suitably dimensioned for mating with the corresponding
convex-shaped tapered surface 24 of lens element L2. Tapered
surface 34 lies between a clear aperture 33 and an outer portion 36
that lies outside clear aperture 33 and extends radially outward
relative to optical axis O. The side and angled views of FIGS. 4
and 5 give a clearer illustration of the various lens element L1
and L2 components.
[0032] Of particular interest is the arrangement and use of outer
portions 26 and 36 for lens elements L2 and L1. Referring to FIG.
6, there is shown, in cross-sectional form, how lens elements L2
and L1 form the tapered fit and the relationship of outer portions
26 and 36. In the embodiment shown in FIG. 6, tapered surfaces 24
and 34 come in contact over a contact area 32. Contact area 32 may
extend over all or most of tapered surfaces 24 or 34. At a minimum,
as shown in the cross sectional view of FIG. 6, contact area 32
extends over only a small segment of tapered surfaces 24 and 34,
defining a circle when lens elements L1 and L2 are axisymmetric, as
in the embodiment of Figures shown in this specification.
[0033] Still referring to FIG. 6, there is a first gap G1 on the
clear aperture 23/33 side of contact area 32 and a second gap G2 on
the opposite side of contact area 32, between outer portions 26 and
36. By providing this clearance of gaps G1 and G2 on opposite sides
of contact area 32, the alignment method used here avoids potential
overconstraint problems that were characteristic of earlier
alignment solutions described in the background section above.
[0034] For achieving optical alignment of lens elements L1 and L2
and maintaining lens elements L1 and L2 in contact with this
tapered fit, within lens barrel 22 as was described with reference
to FIG. 2, a force F is applied in the direction of optical axis O
(along the z axis direction using the coordinate arrangement shown
in FIG. 6). Where lens element L1 is formed from a compliant
material such as plastic, applied force F can even be sufficient to
bend outer portion 36 inward, compressing lens element L1 against
lens element L2 at contact area 32. With sufficient force F, it may
even be possible to compress an outer edge or other part of outer
portion 36 into contact against a corresponding part of outer
portion 26. However, to avoid overconstraint, some gap G2 must be
maintained between outer portions 36 and 26. That is, both gaps G1
and G2 must exist in order to avoid overconstraint.
[0035] It is important to limit any amount of tilt between lenses
L1 and L2, since excessive tilt between lens elements L1 and L2 can
cause significant degradation in the resulting image. Tilt can
occur if lens element L2 becomes tilted with respect to lens
element L1 during some part of the assembly process. This can
happen when lens elements L1 and L2 are brought together at an
excessive contact angle, so that their respective tapered surfaces
34 and 24 do not align as intended. Tapered surface 24 of lens
element L2 and tapered surface 34 of lens element L1 can then
become locked. Even after application of force F as shown in FIG.
6, lens element L2 may remain tilted relative to lens element
L1.
[0036] As one strategy for preventing tilt misalignment at the
interface of tapered surfaces 24/34, supplementary spacing
components can be used. Referring to the close-up view of FIG. 7A,
a compliant spacing member 30 is inserted into gap G2 between outer
portions 36 and 26 of lens elements L1 and L2. Alternately, as
shown in FIG. 7B, compliant spacing member could be inserted into
gap G1, in the space between tapered surfaces 24, 34 and the clear
aperture. This may be preferable, for example, where lens width is
very small.
[0037] In one embodiment, the initial, uncompressed thickness of
compliant spacer member 30 is greater than that of gap G2 (FIG. 7A)
or G1 (FIG. 7B). Because of this, tapered surfaces 24 and 34 are
"pre-aligned" so that gross tilt misalignment is corrected before
tapered surfaces 24 and 34 are mated together. Thus, unintended
locking of tapered surfaces 24 and 34 can be prevented and correct
alignment achieved. In applying force F, as described with
reference to FIG. 6, compliant spacing member 30 can then be
compressed to some degree to suit the desired gap G2 dimensions.
Again, some amount of mechanical compliance would be required in
order to prevent an overconstraint condition. In order to maintain
compression of compliant spacing member 30, retaining ring 13 and
adhesive 14, or an equivalent binding mechanism, would be used as
described with respect to FIG. 2.
[0038] The inner diameter of compliant spacing member 30 preferably
follows the overall shape of the periphery or circumference of
tapered surfaces 24 and 34. Compliant spacing member 30 may be
fabricated from any of a number of suitable materials, including
rubber and plastics. Compliant spacing member 30 need not be
transparent, since it lies outside of the clear aperture 33, 23 of
lens elements L1 and L2. In fabrication, compliant spacing member
30 may be temporarily or permanently bonded to either of lens
elements L1 and L2.
[0039] The taper angle used, shown in FIG. 3 as angle A, may be any
angle suited to the characteristics of the optical apparatus and of
the assembly process. Typically, the taper angle is inclined
between 5 and 70 degrees, but preferably between about 15 and 45
degrees from the optical axis. The taper angle can be provided on
the molded part itself or can be machined into lens element L1 or
L2, using machining techniques such as those conventionally used to
form a bezel. While the taper angles A for tapered surface 24 and
its mating tapered surface 34 may be substantially equal, there may
be advantages in using different angles, as was shown in the cross
section of FIG. 6.
[0040] For best results in aligning lenses L1 and L2 with minimum
tilt with respect to x and y axes, it has proven advantageous to
bring lens elements L1 and L2 into contact by applying a uniform
force, symmetrically distributed with respect to optical axis O.
This force must be sufficient to overcome the friction between lens
elements L1 and L2 over contact area 32 (FIG. 6). In practice,
forces on the order of 2-5 pounds have proved workable for aligning
lens elements L1, L2.
[0041] Using the tapered fit solutions described herein, the
present invention provides an optical system that can be very small
in size and assembled from inexpensively fabricated components,
such as plastic lenses. Because the method of the present invention
avoids the use of a combination of potentially conflicting abutment
and tapered fittings, this method provides a design that is
inherently more forgiving with relation to tolerance errors than
are earlier lens assembly solutions. The method of the present
invention is well suited for use with small-scale optical
assemblies. In an exemplary embodiment, for example, an optical
system such as is shown in FIG. 2 can be assembled to provide
suitable centration and lens spacing for at least two lens
elements. Tilt orthogonal to the optical axis can be carefully
controlled, allowing lens element L1, L2 alignment accurate to
within a few arc-minutes. Once proper alignment is achieved,
further optical component assembly procedures can be carried out to
provide permanence in positioning the optical components, such as
using bonding adhesives, mechanical fasteners, welds such as sonic
or laser welds, or by heat application, for example.
[0042] The apparatus of the present invention allows mounting a
lens element without being overconstrained. As shown in the
enlarged side view of FIG. 2, for example, and as described above,
lens element L2, optically aligned with lens element L1 by means of
the tapered fit of the present invention, does not come in contact
with inner surface 19 of lens barrel 22 or other mounting
structure. The present invention allows the proper orientation of a
lens element, so that a lens element having a specially treated
surface is not inadvertently reversed in assembly, for example.
[0043] While the embodiments of FIGS. 2-6 show optical assemblies
in which two lens elements L1 and L2 are aligned using a tapered
fit, the basic principles outlined above can be extended to use
tapered fits for more than two lenses. FIG. 8 shows a lens assembly
80 in which three lens elements L1, L2, and L3 are all optically
aligned using tapered surfaces. In this case only an outside
diameter 85 of lens element L1 is in contact with an inner surface
89 of a lens barrel 84. An outside diameter 86 of lens element L2
and an outside diameter 87 of lens element L3 are each floating
with respect to inner surface 89. As was described above,
tolerances on these lenses need not be as tightly controlled as
tolerances on lenses that come into contact with the lens barrel or
other mounting structure. Air gaps 88 ensure that lens elements L1,
L2, and L3 are not overconstrained. Of course, taper features can
be used to align four or more optical elements as well. In the
example of FIG. 8, lens element L2 has a pair of convex-shaped
tapered surfaces 72 and 74. Other embodiments using different
arrangements of either convex-shaped or concave-shaped tapered
surfaces are also possible. For example, FIG. 10 shows a lens
assembly 100 in which three lens elements L1, L2, and L3 are
aligned. Here, two lens elements L2 and L3 are aligned within the
concave-shaped tapered surface 91 of lens element L1, thus fitting
lens elements L2 and L3 within the outline of lens element L1.
Tapered surface 91 of lens element L1 extends between its clear
aperture 23 and outer portion 26. Lens element L2 then has tapered
surface 92 that lies in contact against tapered surface 91 for
alignment of lens element L2 with respect to lens element L1.
Similarly, lens element L3 has a tapered surface 93 for alignment
with respect to lens element L1.
[0044] Various arrangements are possible for alignment of one or
more lenses within the lens barrel or other mounting structure,
while one or more additional lenses have a tapered fit. FIG. 9
shows a lens assembly 90 in which a lens element L4 has a tapered
surface 92 that fits over a tapered surface 91 of a lens element
L5. In this case, an outside diameter 94 of lens element L4 comes
in contact with an inner surface 95 of a lens barrel 96. An outside
diameter 93 of lens element L5 floats in space, not coming into
contact with inner surface 95.
[0045] It must be noted that the present invention can be used to
form a compound lens structure in free-standing form, that is, not
yet mounted in a lens barrel, sleeve, or other mounting structure,
using suitable fixtures for assembly.
[0046] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention. For example, lens elements
L1 and L2 need not be axisymmetric as shown in FIGS. 3, 4, and 5.
The tapered fit of the present invention could be applied for lens
elements wherein clear aperture 23,33 has refractive components
that are of various shapes, such as convex, concave, plano, or
meniscus in profile, including clear apertures that are
non-circular, such as those of cylindrical or toroidal lenses, for
example. With non-circular lenses, tapered surfaces would
themselves also be non-circular. While tapered surfaces are shown
extending around the full circumference of clear apertures 23, 33
in the embodiments described above, the tapered surface could
extend only partially around clear aperture 23, 33. One or both
lens elements may be formed from a suitable optical material, such
as glass, plastic, or some composite material.
[0047] Thus it can be seen that the present invention provides an
optical apparatus and method using tapered surfaces to effect
alignment of lens elements.
PARTS LIST
[0048] 10. Lens mount assembly [0049] 12. Spacer [0050] 13.
Retaining ring [0051] 14. Adhesive [0052] 16. Barrel [0053] 17, 18,
21. Outer diameter [0054] 19. Inner surface [0055] 20. Optical
system [0056] 22. Lens barrel [0057] 23. Clear aperture [0058] 24.
Tapered surface [0059] 26. Outer portion [0060] 30. Spacing member
[0061] 32. Contact area [0062] 33. Clear aperture [0063] 34.
Tapered surface [0064] 36. Outer portion [0065] 72, 74. Tapered
surface [0066] 80. Lens assembly [0067] 84. Lens barrel [0068] 85,
86, 87. Outside diameter [0069] 88. Air gap [0070] 89. Inside
surface [0071] 90. Lens assembly [0072] 91, 92, 93. Tapered surface
[0073] 94. Outside diameter [0074] 95. Inner surface [0075] 96.
Lens barrel [0076] 100. Lens assembly [0077] A. Taper angle [0078]
L1, L2, L3, L4, L5. Lens element [0079] G1,G2. Gap [0080] O.
Optical axis
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