U.S. patent application number 12/819134 was filed with the patent office on 2011-06-30 for variable focus lens.
Invention is credited to Chris Miksovsky, Miranda Newbery, Andrew Robertson, Joshua David Silver.
Application Number | 20110157712 12/819134 |
Document ID | / |
Family ID | 37499600 |
Filed Date | 2011-06-30 |
United States Patent
Application |
20110157712 |
Kind Code |
A1 |
Silver; Joshua David ; et
al. |
June 30, 2011 |
VARIABLE FOCUS LENS
Abstract
The invention relates to a variable focus lens (10), comprising
a rigid ring (22), a flexible membrane (20) attached to the front
surface of the ring, a rigid transparent front cover (40), attached
to the flexible membrane (50), and a rigid rear cover (20) on the
rear surface of the ring (22). A cavity (60) is formed between the
flexible membrane (50) and the rear cover (20), and the cavity is
filled with a liquid. The amount of liquid in the cavity can be
varied to vary the curvature of the flexible membrane and so vary
the optical characteristics of the lens. The rear cover can be
integral with the ring, or formed separately. Further, a second
flexible membrane can be positioned between the rear cover and the
ring. The various parts of the lens can be held together by
adhesive.
Inventors: |
Silver; Joshua David;
(Oxford, GB) ; Miksovsky; Chris; (San Francisco,
CA) ; Newbery; Miranda; (Oxford, GB) ;
Robertson; Andrew; (Oxford, GB) |
Family ID: |
37499600 |
Appl. No.: |
12/819134 |
Filed: |
June 18, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12091934 |
Oct 15, 2008 |
7768712 |
|
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PCT/GB2006/004019 |
Oct 27, 2006 |
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12819134 |
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Current U.S.
Class: |
359/666 |
Current CPC
Class: |
G02B 3/14 20130101; G02B
26/004 20130101 |
Class at
Publication: |
359/666 |
International
Class: |
G02B 3/14 20060101
G02B003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 2005 |
GB |
0522030.6 |
Jul 10, 2006 |
GB |
0613688.1 |
Claims
1. A variable focus lens, comprising: a generally rigid ring with a
front surface and a rear surface; a flexible membrane fixed to the
front surface of the ring; a generally rigid transparent front
cover, fixed to the flexible membrane; and a generally rigid rear
cover on the rear surface of the ring; wherein a cavity is formed
between the flexible membrane and the rear cover, the cavity being
filled with a liquid, and wherein the amount of liquid in the
cavity can be varied to vary the curvature of the flexible membrane
and so vary the optical characteristics of the lens.
2. A variable focus lens as claimed in claim 1, wherein the rear
cover and the ring are formed integrally.
3. A variable focus lens as claimed in claim 1, wherein the rear
cover is formed separately from the ring, and is fixed to the rear
surface of the ring.
4. A variable focus lens as claimed in claim 1, wherein the ring,
the flexible membrane and the front cover are fixed by means of
adhesive.
5. A variable focus lens, comprising: a generally rigid ring with a
front surface and a rear surface; a flexible membrane fixed to the
front surface of the ring; a generally rigid transparent front
cover, fixed to the flexible membrane; and a generally rigid rear
cover on the rear surface of the ring, wherein the front cover
and/or the rear cover has a negative or a positive optical power,
and wherein a cavity is formed between the flexible membrane and
the rear cover, the cavity being filled with a liquid, and wherein
the amount of liquid in the cavity can be varied to vary the
curvature of the flexible membrane and so vary the optical
characteristics of the lens.
6. A variable focus lens, comprising: a generally rigid ring with a
front surface and a rear surface; a flexible membrane fixed to the
front surface of the ring; a generally rigid transparent front
cover, fixed to the flexible membrane; and a generally rigid rear
cover on the rear surface of the ring; wherein a cavity is formed
between the flexible membrane and the rear cover, the cavity being
filled with a liquid, and wherein the amount of liquid in the
cavity can be varied to vary the curvature of the flexible membrane
and so vary the optical characteristics of the lens, and wherein
the refractive index of the liquid in the cavity is approximately
equal to the refractive index of the material from which the rear
cover is formed.
7. A variable focus lens, comprising: a generally rigid ring with a
front surface and a rear surface; a flexible membrane fixed to the
front surface of the ring; a generally rigid transparent front
cover, fixed to the flexible membrane; a generally rigid rear cover
on the rear surface of the ring; and a second flexible membrane
positioned between the ring and the rear cover, such that the
second flexible membrane is fixed to the rear surface of the ring
and the rear cover is fixed to the second flexible membrane;
wherein a cavity is formed. between the flexible membrane and the
rear cover, the cavity being filled with a liquid, and wherein the
amount of liquid in the cavity can be varied to vary the curvature
of the flexible membrane and so vary the optical characteristics of
the lens.
8. A variable focus lens as claimed in claim 7, wherein the ring,
the second flexible membrane and the rear cover are fixed by means
of adhesive.
9. A variable focus lens, comprising: a generally rigid ring with a
front surface and a rear surface; a flexible membrane fixed to the
front surface of the ring; a generally rigid transparent front
cover, fixed to the flexible membrane; a generally rigid rear cover
on the rear surface of the ring, wherein a cavity is formed.
between the flexible membrane and the rear cover, the cavity being
filled with a liquid, and wherein the amount of liquid in the
cavity can be varied to vary the curvature of the flexible membrane
and so vary the optical characteristics of the lens; and wherein a
vent hole is formed in the front cover to allow air in and out of
the cavity.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 12/091,934, filed on Oct. 27, 2006, now allowed, which claims
priority to Great Britain Patent Application Nos. 0522030.6, filed
Oct. 28, 2005 and 0613688.1 filed Jul. 10, 2006, the contents of
all of which are incorporated herein by reference in their
entirety.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates to a variable focus lens, and
more particularly to a variable focus lens of simple construction
suitable for mass-production. Variable focus lenses are well known.
They normally consist of a liquid-filled chamber, at least one face
of which is formed by a transparent flexible membrane. As liquid is
introduced into or removed from the chamber, the flexible membrane
is deformed, and its curvature accordingly changes. This change in
curvature leads to a change in the optical characteristics and
power of the lens. The power of the lens can thus be varied simply
by varying the amount of liquid in the chamber.
[0004] 2. Description of the Related Art
[0005] A related art variable focus lens is disclosed, for example,
in GB 2333858. This lens is formed from several interengaging
rings. Flexible transparent membranes are trapped between the
rings, and the rings are formed such that as they interengage, they
serve to tension the flexible membranes (which improves the
performance of the lens). One of the rings is then deformed to hold
the assembly together. However, this design places certain
requirements (such as ductility) on the materials used to form the
rings, and also requires strict tolerances in the manufacturing of
the rings. Further, each lens is formed from a large number of
separate parts, which complicates manufacture.
SUMMARY
[0006] According to the invention, there is provided a variable
focus lens, comprising: a generally rigid ring with a front surface
and a rear surface; a flexible membrane attached to the front
surface of the ring; a generally rigid transparent front cover,
attached to the flexible membrane; and a generally rigid rear cover
on the rear surface of the ring; wherein a cavity is formed between
the flexible membrane and the rear cover, the cavity being filled
with a liquid, and wherein the amount of liquid in the cavity can
be varied to vary the curvature of the flexible membrane and so
vary the optical characteristics of the lens.
[0007] In the lens of the invention, the flexible membrane is held
between the ring and the front cover, which may be formed with flat
faces. This places less stringent requirements regarding tolerances
on the parts of the lens, and so simplifies manufacture. Further,
there is a wider choice of materials from which the lens can be
formed.
[0008] In a preferred form, the rear cover and the ring are formed
integrally, for example by moulding as a single piece. This reduces
the number of steps required to assemble the lens. However, this is
not a necessary feature, and in an alternative form, the rear cover
is formed separately from the ring, and is attached to the rear
surface of the ring.
[0009] In a further alternative form, the lens additionally
comprises a second flexible membrane positioned between the ring
and the rear cover, such that the second flexible membrane is
attached to the rear surface of the ring and the rear cover is
attached to the second flexible membrane. Such a lens has twice as
much power as a single-membrane lens for a given lens cavity
pressure (or allows the same power with half the cavity
pressure).
[0010] Further, it will be appreciated that in all of these lenses,
the flexible membranes are protected from damage, as they are
behind rigid covers. The durability and toughness of the lenses is
thus improved.
[0011] When the curvature of the flexible membrane is varied, the
volume of the space between the flexible membrane and the front
cover changes. As air is a gas, and so compressible, it is possible
for movement of the flexible membrane to be accommodated by
compression or rarefaction of the air in this volume. However, it
is preferred for a vent hole to be formed in the front cover, to
allow air in and out of the cavity.
[0012] The ring has a section through which liquid can be
introduced into or withdrawn from the cavity. In a preferred form,
this section is formed as a septum positioned in an opening in the
ring. The septum is preferably formed from a self-healing material,
which allows liquid to be introduced into and removed from the
cavity by means of a syringe needle or the like inserted through
the septum.
[0013] In a further preferred form, two or more septa are provided.
This makes it easier to fill the cavity, as a needle pushed through
one septum can be used to introduce liquid, and a needle pushed
through the other septum can be used to withdraw air.
[0014] Preferably, the front cover and/or the rear cover has a
negative or positive optical power.
[0015] It is also preferred for the refractive index of the liquid
in the first cavity to be approximately equal to the refractive
index of the material from which the rear cover is formed. This
reduces the visibility of any flaws, scratches and the like on the
inside of the rear cover.
[0016] Of course, any suitable method can be used for holding the
ring, the flexible membrane and the covers together. However, it is
preferred for the ring, the, flexible membrane and the front cover
are attached by means of adhesive. Further, when there is a second
flexible membrane between the ring and the rear cover, it is
preferred that the ring, the second flexible membrane and the rear
cover are attached by means of adhesive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Preferred embodiments of the invention will now be described
by way of example only and with reference to, the accompanying
drawings, in which:
[0018] FIG. 1 is a perspective view of a first preferred embodiment
of the lens;
[0019] FIG. 2 is a side view of the lens;
[0020] FIG. 3 is a front view of the lens;
[0021] FIG. 4 is a cross-sectional view of the lens taken along
line A-A in FIG. 3;
[0022] FIG. 5 is a cross-sectional view of a second embodiment of
the lens; and.
[0023] FIG. 6 is a cross-sectional view of a third embodiment of
the lens.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0024] As best shown in FIG. 4, the lens 10 is formed from three
main parts: a rear part 18, a front cover 40 and a flexible
membrane 50.
[0025] The rear part 18 is in the form of a shallow dish, formed
from a ring 22 and a rear cover 20 integrally formed with the ring.
The flexible membrane 50 extends across the face of the shallow
dish, and is attached to the front surface of the ring 22. The
cavity 60 formed between the dish and the flexible membrane 50 is
filled with a liquid, and the amount of liquid in the cavity 60 can
be varied to change the volume of the cavity 60. The ring 22 and
the rear cover 20 are generally rigid, and so changing the volume
of the cavity 60 deforms the membrane 50 and thus varies the
optical characteristics of the lens 10.
[0026] The front cover 40 is attached to the membrane 50, so that
the membrane 50 is sandwiched between the ring 22 and the front
cover 40. A second cavity 70 is formed between the membrane 50 and
the front cover 40, and this cavity 70 contains air. A small vent
hole 44 is formed in the front cover 40 and allows the second
cavity 70 to communicate with the atmosphere. This allows the
volume of air in the second cavity 70 to vary as the membrane 50
deforms. The vent hole 44 is positioned at the edge of the lens,
and is as small as possible, to reduce any distraction caused to
the user of the lens.
[0027] As shown in the drawings, the inner surface 42 of the front
cover 40 (the surface facing the flexible membrane 50) is curved.
This provides sufficient space for the flexible membrane 50 to be
deformed, and thus allows the power of the lens 10 to be
adjusted.
[0028] There is an opening 24 in the ring 22 of the rear part (best
seen in FIG. 1), and this opening 24 is normally sealed by a
flexible plug 80 (hereinafter referred to as a "septum"). The
septum 80 prevents liquid from leaking out of the cavity 60, and
also prevents air leaking into the cavity 60, and so maintains the
curvature of the membrane 50 (and so the optical characteristics of
the lens 10) in a desired state.
[0029] The septum 80 is formed from a self-healing material. Such
materials can be pierced by needles or the like, and reseal on
removal of the needle. The use of such a material allows the amount
of liquid in the cavity 60 to be adjusted through the use of such a
needle.
[0030] To increase the amount of liquid in the cavity 60, the
needle of a syringe containing liquid is pushed through the septum
80, so that the end of the needle penetrates the cavity 60. Liquid
is then pushed from the syringe into the cavity 60. The increase in
the amount of liquid forces the flexible membrane 50 to bow further
outwards, changing the optical characteristics of the lens. Once
the desired optical characteristics have been achieved, the needle
is withdrawn from the cavity 60 and the septum 80. Because of the
self-healing nature of the septum 80, the hole formed by the needle
closes up, and the cavity 60 is sealed again.
[0031] A similar procedure is used to withdraw liquid from the
cavity 60.
[0032] In order to ensure a good seal between the septum 80 and the
opening 24 in the ring 22, the septum 80 can be inserted into the
opening 24 while under tension, and then allowed to relax. When the
septum 80 is put under tension, it stretches in a longitudinal
direction, and so contracts in a lateral direction as a result of
Poisson's ratio. While laterally contracted, the septum 80 can be
correctly positioned in the opening 24, and the tension can then be
released. The release of tension causes the septum 80 to return to
its original width, which is ideally slightly greater than the
width of the opening 24, to securely hold the septum 80 in
place.
[0033] In an alternative form, the septum could be co-moulded with
the rear part 18. In this method, the rear part is first moulded
from a plastic material, with the opening in the ring being formed
in this moulding step. Then, a plug of elastomer is moulded into
the opening in a second moulding step, and this plug forms the
septum. The materials used to form the rear part and the septum
would be chosen so that they have good natural bonding, to ensure
the septum stays firmly seated in the opening. It will be
appreciated that such a co-moulding process could produce rear
parts with septa more quickly and more cheaply than the two-step
method described above.
[0034] In a preferred form, the front cover 40 is-formed as a lens
(i.e. the curvatures of its front surface and back surface are
different). This allows the variable focus lens to have a greater
maximum power (or a different range of powers) than could be
achieved solely by deforming the flexible membrane 50.
[0035] For example, suppose that the range of powers that can be
achieved solely by deforming the flexible membrane is from -5 D to
+5 D. If a user requires a correction outside this range (say, -8
D), then this cannot be achieved solely by deforming the flexible
membrane. However, by providing the front cover with some lens
power (say, -5 D), the range of available powers is shifted to
become from -10 D to 0 D, which covers the required correction. In
a similar manner, if a higher positive power is required, this can
be achieved by providing the front cover with some positive lens
power.
[0036] Further, in some situations, it is desirable to ensure that
the pressure of the liquid inside the cavity is above (or at least
equal to) atmospheric pressure. If this pressure is maintained,
then the flexible membrane will bow outwardly, which will tend to
give the lens a positive power. If the lens as a whole is to
provide a negative power, then this must be achieved by providing
at least one of the front cover and the rear cover with a negative
power.
[0037] A currently preferred process for manufacturing the variable
focus lens will now be described.
[0038] Firstly, the rear part 18 is formed, for example by moulding
acrylic, or by machining and polishing. Depending on the quality of
the moulding, the surface 26 which in use faces the user's eye can
be left in its as-moulded form; alternatively, this surface 26 may
be polished to improve its smoothness. The interior surfaces 28, 30
are also machined to shape. The opening 24 for the septum 80 can be
formed in the moulding process, or it can be machined after
moulding. A combination of moulding and machining can also be used
to form the opening 24.
[0039] The septum 80 is then formed from cast silicone. In a
preferred form, the cast silicone has a Shore hardness of between
30 A and 40 A. The silicone septum is then primed (for example, by
brushing on Loctite 770 primer), and a cyanoacrylate glue (such as
Loctite 403) is applied to it.
[0040] The septum 80 is then pulled into the opening 24 in the rear
cover. This pulling stretches the septum 80, and so causes it to
reduce in width, allowing it to fit into the opening 24. Once the
septum 80 is positioned correctly, the tension is released, and the
septum attempts to return to its original size, which causes it to
seat firmly in the opening 24. This ensures a good seal between the
septum 80 and the opening 24.
[0041] Any excess glue is then wiped away from the septum 80.
Further, once the glue has cured, the inwardly-protruding "tail" of
the septum is trimmed away, so that the septum is flush with the
inner wall 30 of the ring 22. This reduces the intrusion of the
septum 80 into the visual field of the user.
[0042] The flexible membrane 50 is then prepared. In a preferred
form, this is made from a sheet of polyester film such as Mylar,
and in particular from Mylar DL, which has good optical qualities.
The sheet can also be treated (on one or both sides) to improve its
adhesion qualities. The sheet is then put under tension.
[0043] A thin bead of ultraviolet-curing adhesive (such as Loctite
3105) is applied to the front surface 32 of the ring 22 which will,
in the assembled state, confront the front cover 40 (and contact
the membrane 50). The front surface of the ring 22 of the part 18
is then rested on the sheet, so that the adhesive comes into
contact with the sheet.
[0044] The assembly of the rear part 18 and the sheet is then
exposed to an ultraviolet light source to cure the adhesive. This
can be any suitable source, and it is possible to simply expose the
assembly to bright sunlight to cure it.
[0045] Once the adhesive is cured, the sheet is cut to match the
contour of the ring 22. This may be done in two phases; a first
rough-cut phase, to release the assembly from the rest of the
sheet, and a second trimming phase, in which the part of the sheet
adhered to the ring is trimmed to match the ring.
[0046] The front cover 40 is then formed. Any suitable method and
material can be employed; in a preferred form, the front cover 40
is moulded or machined and polished from polycarbonate. The front
cover 40 may also be formed from a standard moulded spectacle lens,
cut to the appropriate shape.
[0047] It will be noted that the front covet 40 and the ring 22 of
the rear part 18 are both formed with two diametrically opposed
longitudinal grooves 34, 46 in their side surfaces. These grooves
34, 46 serve to ensure that the front cover 40 and rear part 18 are
correctly aligned during their assembly, which will now be
described.
[0048] During assembly, the assembly of the rear part 18 and the
membrane 50 is fitted into an indexing feature, membrane 50
upwards. This feature has two projecting ridges, which engage with
the grooves 34 on the rear part 18. When the rear part 18 is
properly fitted into the indexing feature, its position is defined
by the engagement of the ridges with the grooves 34.
[0049] Of course, other indexing features could-be used, for
example, a jig with counterbores that reference the outer profile
of the covers. This may be preferable in some cases, as the grooves
34, 46 can have an impact on the aesthetics of the lens.
[0050] A thin bead of ultraviolet-curing adhesive (such as Loctite
3105) is applied to the surface 48 of the front cover 40 which
will, in the assembled state, confront the ring 22 (and contact the
membrane 50). It will be appreciated that this step can take place
before or after the assembly of the rear part 18 and the membrane
50 is fitted into the indexing feature.
[0051] The front cover 40 is then also fitted into the indexing
feature, adhesive side downwards. It rests on the membrane 50, so
that the adhesive comes into contact with the membrane, and as
before, is exposed to ultraviolet light (which may again be
sunlight) to cure the adhesive.
[0052] Once the adhesive has cured, the lens assembly 10 is removed
from the indexing feature. The cavity 60 formed between the rear
cover 20, the ring 22 and the membrane 50 is filled with a liquid
such as oil by means of a needle inserted through the septum 80,
and adjustment of the amount of liquid in the cavity 60 to achieve
correct focus of the lens 10 can be carried out at this stage.
[0053] Once the cavity 60 is filled with oil, the outer side of the
septum 80 is trimmed away, so that the septum 80 is flush with the
outer wall of the ring 22. This gives the lens 10 a smooth outer
contour, and makes it easier to fit the lens into spectacle
frames.
[0054] As a final step, two such lenses are fitted into a frame, to
produce a pair of spectacles. If desired, the frames can
have-openings, aligned with the septa of the lenses, to allow a
needle to be inserted through the frame and the septum of a lens to
allow further fine adjustment of the focus of the lens.
[0055] In the lens described above, there is a single opening 24 in
the ring 22 of the rear part 18, closed by a single septum 80. In
an alternative form, the side wall of the rear cover can have two
openings, each closed by a septum.
[0056] This twin-septum design has a number of advantages with
regard to filling the cavity. For example, if the septa are
generally diametrically opposite each other, then the lens can be
positioned with one septum above the other. Liquid can be
introduced into the cavity by means of a needle pushed through the
lower septum, and air can be withdrawn from the cavity by means of
a second needle pushed through the upper septum. This filling
method reduces the number of air bubbles in the cavity once it is
filled with liquid, and so improves the optical quality of the
lens.
[0057] It is preferred that the refractive index of the liquid in
the cavity 60 is approximately equal to the refractive index of the
material used to form the rear cover 20.
[0058] As mentioned above, some machining of the rear part 18 is
required to bring it to the desired shape, and in particular, the
surface 28 of the rear cover 20 which forms part of the cavity is
machined. It is possible to machine this surface 28 in such a way
as to avoid scratches; however, this requires expensive machining
processes, and this leads to an increase in the cost of the lens
10.
[0059] A cheaper approach is to ensure that the refractive indices
of the liquid and the rear cover material are approximately equal.
If this is so, then there will be no refraction of a light ray
passing from the liquid into the rear cover, and any scratches on
the surface of the rear cover will be effectively invisible.
[0060] It will be appreciated that the above detailed description
is only concerned with one particular structure of lens, and other
similar structures can be used. Two such structures will now be
briefly described with reference to FIGS. 5 and 6.
[0061] In the lens 110 shown in FIG. 5, the rear cover 120 and the
ring 122 are formed as separate parts, and are attached to each
other by adhesive. This can be a first step in the assembly process
described above, prior to formation and attachment of the septum.
The flexible membrane 150, the front Cover 140 and the cavity 160
are all analogous to those shown in FIG. 4.
[0062] In the lens 210 shown in FIG. 6, the rear cover 220 and the
ring 222 are again formed as separate parts. Further, a second
flexible membrane 252 is positioned between the ring 222 and the
rear cover 240 (which is will be seen is curved to allow the
membrane to deform). Thus, the cavity 260 is defined by the
flexible membranes 250, 252 and the ring 222.
[0063] The presence of two membranes gives the lens twice, as much
power as a single-membrane lens for a given lens cavity pressure
(or allows the same power with half the cavity pressure). Although
such a lens may be thicker than the lens shown in FIGS. 1 to 5,
this may not be consequence, depending on the use to which the lens
is put (for example, in instruments).
* * * * *