U.S. patent application number 10/190415 was filed with the patent office on 2002-12-26 for wetcell device for inspection.
Invention is credited to Chiang, Shiao-Tsing David, Russell, Todd Aldridge.
Application Number | 20020196429 10/190415 |
Document ID | / |
Family ID | 23465277 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020196429 |
Kind Code |
A1 |
Russell, Todd Aldridge ; et
al. |
December 26, 2002 |
Wetcell device for inspection
Abstract
The invention provides an inspection cell for inspecting an
ophthalmic lens. The inspection cell is a solid block that has a
bottom planar surface, a top surface, and an indentation in the top
surface. The indentation is adapted to receive an ophthalmic lens.
which is to be inspected. The invention additionally provides an
inspection unit for an ophthalmic lens, which holds one or more of
the inspection cells.
Inventors: |
Russell, Todd Aldridge;
(Lawrenceville, GA) ; Chiang, Shiao-Tsing David;
(Roswell, GA) |
Correspondence
Address: |
Thomas Hoxie
Novartis Corporation
Patent and Trademark Dept.
564 Morris Avenue
Summit
NJ
07901-1027
US
|
Family ID: |
23465277 |
Appl. No.: |
10/190415 |
Filed: |
July 3, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10190415 |
Jul 3, 2002 |
|
|
|
09858394 |
May 16, 2001 |
|
|
|
09858394 |
May 16, 2001 |
|
|
|
09371753 |
Aug 10, 1999 |
|
|
|
6259518 |
|
|
|
|
Current U.S.
Class: |
356/124 |
Current CPC
Class: |
G01M 11/0214 20130101;
G01B 11/255 20130101 |
Class at
Publication: |
356/124 |
International
Class: |
G01B 009/00 |
Claims
What is claimed is:
1. An inspection cell for an ophthalmic lens, comprising a solid
block having a bottom planar surface and a top surface, wherein
said top surface has a concave indentation, wherein said concave
indentation is adapted to accept said ophthalmic lens.
2. The inspection cell of claim 1, wherein said indentation is
hemispherical, hemielliptical or conical.
3. The inspection cell of claim 2, wherein said indentation has an
apex and said apex has a radius at least about 15% larger than the
radius of said ophthalmic lens.
4. The inspection cell of claim 1, wherein said indentation is
hemispherical.
5. The inspection cell of claim 1, wherein said bottom planar
surface and the surface of said concave indentation are optically
finished.
6. The inspection cell of claim 1, wherein said bottom planar
surface and the surface of said concave indentation are optically
finished, and said inspection cell comprises a transparent
material.
7. The inspection cell of claim 6, wherein said transparent
material is quartz, glass, polymethylmethacrylate, polycarbonate,
polystyrene, polyester, methylpentene or nylon.
8. The inspection cell of claim 6, wherein said transparent
material is quartz.
9. An inspection unit for inspecting an ophthalmic lens, comprising
an inspection cell which comprises a solid block having a bottom
planar surface and a top surface, wherein said top surface has a
concave indentation, wherein said concave indentation is adapted to
accept said ophthalmic lens and to center said ophthalmic lens in
said indentation.
10. The inspection unit of claim 9, wherein said inspection unit
further comprises an inspection cell carrier.
11. The inspection unit of claim 10, wherein said inspection cell
carrier holds a multitude of said inspection cells.
12. The inspection unit of claim 9 wherein said concave indentation
is hemispherical, hemielliptical or conical.
13. The inspection cell of claim 9, wherein said indentation has an
apex and said apex has a radius at least about 15% larger than the
radius of said ophthalmic lens.
14. The inspection unit of claim 9, wherein said indentation is
hemispherical.
15. The inspection unit of claim 9, wherein said bottom planar
surface and the surface of said concave indentation are optically
finished.
16. The inspection unit of claim 9, wherein said bottom planar
surface and the surface of said concave indentation are optically
finished, and said inspection cell comprises a transparent
material.
17. The inspection unit of claim 16, wherein said transparent
material is quartz.
18. A reusable inspection cell for a hydrogel contact lens,
comprising a quartz block having an optically finished bottom
planar surface and a top surface, wherein said top surface has an
optically finished concave indentation, wherein said concave
indentation is adapted to accept said contact lens.
19. The inspection cell of claim 18, wherein said concave
indentation is hemispherical, hemielliptical or conical.
20. The inspection cell of claim 18, wherein said indentation is
hemispherical.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a device that receives an
ophthalmic article for an inspection.
[0002] Conventional production methods for producing ophthalmic
lenses, e.g., contact lenses and intraocular lenses, include lathe
cutting methods and cast molding methods. A lathe cutting method
produces an ophthalmic lens by cutting a solid substrate of a
polymeric optical material to a designed shape. A cast molding
method uses a molding process to produce an ophthalmic lens.
Typically, a lens mold having two mold halves. i.e., a front curve
mold half and a back curve mold half, is used to mold a lens from a
polymerizable liquid composition. Once the lens is produced and
before it is packaged. the lens is inspected for flaws and damages
that may be created or included during the production process.
[0003] Typically, a finished lens is inspected before the lens is
packaged for sale. The inspection process for ophthalmic lenses,
especially hydrogel lenses, e.g., polyhydroxyethylmethacrylate
contact lenses, is highly arduous since a typical ophthalmic lens
is transparent, and therefore, it is difficult to locate the lens,
let alone inspect the lens, especially when the lens is placed in a
transparent liquid, such as water or saline solution. A
conventional process for inspecting a hydrogel lens is a manual
process that places the lens in a Petri dish and visually inspects
the lens under a magnifying projection device. A human inspector
must place the lens in a Petri dish under a magnifying projection
device and locate the lens in the dish before the inspector can
begin the visual inspection.
[0004] As for an automated machine vision inspection system, a lens
is placed in a cell and then the cell is placed under a CCD camera
to take a digital image of the lens. The digital image is analyzed
with a microprocessor to detect defects in the lens. For example,
U.S. Pat. No. 5,443,152 discloses an automated inspection system
for a contact lens that uses an inspection cell. The patent teaches
a disposable conical cell for transporting and inspecting a contact
lens. Although the conical inspection cell is useful the conical
shape of the inspection cell highly or nonuniformly distorts the
inspection light as the light passes through various sections of
the cell.
[0005] There remains a need for an inspection cell that ensures
predictable placement of a lens placed therein and does not highly
and nonuniformly distort inspection light, thereby allowing a
simple inspection system to be used to inspect the lens.
SUMMARY OF THE INVENTION
[0006] There is provided in accordance with the present invention
an inspection cell, more particularly an inspection wetcell,
suitable for inspecting an ophthalmic lens, e.g., a contact lens.
The inspection cell is a solid block that has a bottom planar
surface, a top surface, and an indentation in the top surface. The
indentation is adapted to receive an ophthalmic lens and to place
the lens in the center of the viewing field. The invention
additionally provides an inspection unit for an ophthalmic lens.
The inspection unit holds one or more of the inspection cells.
[0007] The inspection cell of the present invention allows an
opthalmic lens to settle to the bottom of the indentation of the
inspection cell and allows light to transmit through the cell
without significant optical distortion once a carrier liquid is
placed in the indentation. Accordingly, the inspection cell is
highly suitable for conducting an automated or a manual inspection
of an ophthalmic lens with a relatively simple inspection
system.
DESCRIPTION OF THE DRAWING
[0008] FIG. 1 illustrates an exemplary inspection cell of the
present invention.
[0009] FIG. 2 illustrates a cutaway side view of an inspection
cell.
[0010] FIG. 3 illustrates the field of inspection for an inspection
cell.
[0011] FIG. 4 illustrates an inspection unit having an inspection
cell and a carrier.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The present invention provides an inspection cell for
inspecting an ophthalmic lens, especially a hydrogel ophthalmic
lens. The inspection cell is a block of a transparent or
translucent solid material, and the block has a concave indentation
in the upper surface such that an ophthalmic lens can be placed in
the indentation. The indentation of the cell has a dimension that
ensures the ophthalmic lens placed therein descends to and settles
at or around the center or apex of the indentation when the
indentation is filled with appropriate fluid. According to the
present invention. an ophthalmic lens placed in the inspection cell
is inspected for flaws, e.g., tears and flash. and inclusions of
extraneous materials, e.g., air bubbles, using a manual or machine
vision inspection system.
[0013] FIG. 1 illustrates an exemplary inspection cell of the
present invention. Although FIG. 1 illustrates the present
invention in conjunction with a cylindrical inspection cell for a
contact lens, the inspection cell can have other side wall
configurations and base shapes, e.g., cubical, and other ophthalmic
lenses, e.g.. interocular lens, can be inspected in the cell. The
inspection cell 10 has a concave indentation 12, which is adapted
to receive and hold an ophthalmic lens, especially a contact lens.
The inspection cell 10 has a cylindrical sidewall 14, an upper
planar surface 16 and a lower planar surface 18. Preferably, the
upper planar surface 16 and the lower planar surface 18 are
parallel to each other, and the lower planar surface 18 and the
surface of the concave indentation are optically finished, i.e.,
highly polished. such that imperfections on these surfaces do not
randomly scatter light and do not interfere with the inspection
process. The suitable level of optical finish has scratch and dig
values preferably up to 40/20, more preferably up to 20/10, in
accordance with the U.S. Military Specification for the inspection
of Optical Components, MIL-O-13830A.
[0014] As for the concave indentation 12, it has a shape that
allows a contact lens to easily and reliably settle to or near the
apex 20 of the concave indentation 12 when the lens is placed in
the opening of the indentation 12. Suitable shapes for the concave
indentation 12 include hemispherical, hemielliptical and bowl
shapes. A suitable indentation can also have a combination of
shapes, such as a frustoconical wall with a hemispherical apex.
Preferably, a suitable indentation for the present invention has a
symmetrical inwardly curved sidewall that forms a smooth converging
region at center of the indentation. As a preferred embodiment of
the present invention, the concave indentation has a hemispherical
shape. The term "hemispherical" as used herein indicates a
configuration that is a portion of a sphere, including a half
sphere. The hemispherical shape is desirable in that the
symmetrical circular shape does not require highly precise
positioning and orientation of the indentation when fabricating the
inspection cell and using the cell for inspection. For example,
even when the two planar surfaces of an inspection cell are not
parallel to each other and a hemispherical indentation is formed
with respect to the upper surface, the symmetrical configuration of
a hemispherical ensures that there is only one apex when the cell
is horizontally placed with respect to the lower surface.
[0015] To facilitate the settling movement of the contact lens, the
radius of the curvature of the concave indentation, especially near
the apex 20, should be larger than the radius of the front curve of
the contact lens. Preferably, when a hydrogel soft contact lens is
inspected in the inspection cell 10, the radius near the apex 20 is
at least about 15% larger than the radius of the front curve of the
lens. More preferably, the radius near the apex 20 is at least
about 20% larger than but less than about 400%, even more
preferably at least about 50% larger than but less than about 200%,
of the radius of the front curve of the lens. Reliably settling the
lens 30 to the apex 20 within a range of tolerance is highly useful
for the inspection process since the location of the lens 30 in the
inspection cell 10 becomes predictable.
[0016] According to the present invention, the size or volume of
the concave indentation 12 should be large enough to completely
contain the contact lens placed therein. More specifically, the
concave indentation 12 should be large enough to hold an amount of
a carrier liquid, e.g., water or a saline solution, such that the
contact lens is completely submerged in the liquid. Preferably, the
overall volume of the concave indentation 12 is between about 600%
and about 100%, more preferably between about 550% and about 200%,
most preferably between about 500% and about 300%, larger than the
volume of the hemisphere formed by the contact lens. The use of a
carrier liquid is important for hydrogel contact lenses since a
hydrogel lens by itself does not have sufficient rigidity to retain
its natural configuration. The carrier liquid provides support to
make the lens self-supportive and allows the lens to exhibit its
proper shape, making possible proper inspection of the lens.
Additionally, the carrier liquid allows the lens to settle to the
apex of the concave indentation 12. FIG. 2 illustrates a cutaway
side view of the inspection cell 10 with a contact lens 30 in the
concave indentation 12. The lens 30 is submerged in a carrier
liquid 32 such that the shape of the lens 30 is not distorted and
the lens 30 can be inspected.
[0017] Suitable carrier liquids include water, e.g., deionized
water, and isotonic solutions that are compatible with the eye,
e.g., sodium chloride saline and polysaccharide solutions. The
carrier liquid may also contain additives that facilitate the
inspection process, provide that the additives do not significantly
reduce the clarity of the carrier liquid. For example, the carrier
liquid may contain a small amount of a surfactant to facilitate the
movement of the lens in the inspection cell and to avoid trapping
air bubbles on the lens or the surface of the indentation of the
inspection cell.
[0018] In accordance with the present invention, the inspection
cell is produced from a transparent or translucent material,
depending on the type of inspection system used. A transparent or
substantially transparent solid material is preferred for the
present inspection cell. As a preferred embodiment, the solid
material for the inspection cell is transparent and has a
transmission efficiency of at least about 80%, preferably at least
about 85%, more preferably at least about 90%, most preferably at
least about 95%, for visible light.
[0019] Suitable materials for the inspection cell include quartz,
glass and thermoplastic polymers, and suitable thermoplastics
include polycarbonate, polystyrene, polyethylene, polypropylene,
polyester, polymethylmethacrylate, methylpentene, nylon and the
like, as well as transparent and translucent copolymers thereof. Of
these suitable solid materials. thermoplastic materials are
preferred, transparent thermoplastic materials are more preferred,
if a disposable inspection cell is desired; and quartz is preferred
if a reusable inspection cell is desired. As a preferred embodiment
of the present invention, a suitable solid material for the
inspection cell has an index of refraction or a refractive index
that is not highly different from the carrier liquid. e.g., water
or a saline solution. Preferably, the difference in the refractive
indices between the solid material and the carrier liquid is less
than about 20%. more preferably less than about 15%, based on the
refractive index of the cell. The similarity in the refractive
indices of the inspection cell and the carrier liquid is highly
useful since inspection light that transverses the interface
between the inspection cell and the carrier liquid is not
significantly distorted or refracted when the two materials have
similar refractive indices. It is to be noted that the distortion
of the path of inspection light caused by the inspection cell can
be optically corrected with a system of optical lenses, provided
that the distortion is not significant and highly nonuniform. For a
reusable inspection cell, quartz is particularly suitable present
invention since quartz has a refractive index which is not highly
different from the refractive indices of water and isotonic saline
solutions and is highly abrasion resistant such that the inspection
cell provides undistorted images and can be reused for repeated
inspection cycles. In addition, quartz has a hydrophilicity that
allows an aqueous liquid to form a flattened meniscus, thereby
further preventing distortion of the path of the light.
[0020] Returning to FIG. 2, the inspection cell 10 contains the
contact lens 12 in a carrier liquid 32, e.g., an isotonic saline
solution. When inspection light, which can be scattered light or
collimated light depending on the type of the inspection system, is
projected through the lower surface 18 of the inspection cell, the
light passes through the inspection cell as well as through the
contact lens 30 and the carrier liquid 32. The light exiting the
carrier solution above the contact lens is then manually observed
with a projection magnifier or analyzed with a machine vision
system for the presence of any flaws and inclusions in the contact
lens. Since the inspection cell 10 and the carrier liquid 32 do not
have highly different refractive indices, the path of the light
passing entering the carrier liquid 32 from the inspection cell 10
is not highly distorted, i.e., not highly refracted, even though
the interface between the two materials forms a concave surface.
Alternatively stated, when the lens is placed in the inspection
cell 10 without the carrier liquid 32, the image of the contact
lens 30 will be significantly distorted since the concave surface
of the indentation 12 causes the inspection cell 10 to act as a
concave optical lens.
[0021] When the carrier liquid is placed in the indentation 20, the
inspection cell essentially forms an optical block from the lower
planar surface 18 to the top surface of the carrier liquid.
Consequently, light passing through the inspection cell and the
carrier liquid is not significantly distorted, and the light
projected through the inspection cell can be simply analyzed using
an automated or manual inspection system. In contrast, typical
prior art inspection cells for an automated inspection, for example
disclosed in U.S. Pat. No. 5,443,152 to Davis, have a curved outer
surface at the apex of the indentation, and therefore, such an
inspection cell significantly distorts the path of the light.
Accordingly, the light passing through such a prior art inspection
cell needs to be optically manipulated to correct the distortion
with an elaborate corrective optical system.
[0022] It has been found that an uncontrolled formation of the
meniscus by the carrier liquid in the inspection cell may interfere
with the path of the inspection light. Accordingly, the location of
the meniscus, especially the edge of the meniscus, should be
controlled, for example, by placing the edge of the meniscus away
from the field of inspection. FIG. 3 illustrates an exemplary set
up for controlling the meniscus 40 formed by the carrier liquid
against the concave surface of the hydrophobic inspection cell 10.
The opening of the indentation of the inspection cell 10 in FIG. 3
has a diameter which is larger than the field of inspection 42 such
that the bent peripheral edge of the meniscus 40 is located away
from the field of inspection 42. When the inspection light 44
passes through the inspection cell 10, the lens 30 and the carrier
liquid 32, only the portion of the light that is in the field of
inspection 42 is captured by the inspection camera, if an automated
inspection system is used, or by the viewing lens, if a manual
inspection system is used. Accordingly, by limiting the viewing
section over the meniscus or increasing the size of the opening of
the indentation, thereby placing the bent edge of the meniscus to
be outside of the field of inspection, the image distorting effect
of the meniscus can be avoided.
[0023] Alternatively, the inspection cell can have an extended wall
above the opening of the indentation, e.g., a cylindrical wall,
which has a larger diameter than the opening of the indentation.
When the carrier liquid is over filled in the indentation, the
extra liquid over the opening of the indentation forms a meniscus
along the extended wall away from the field of inspection. which is
equal to or smaller than the opening of the indentation of the
inspection cell.
[0024] FIG. 4 illustrates another exemplary set up for controlling
the image distorting effect of the meniscus. The inspection cell 10
is placed in a cell carrier 50, forming an inspection unit. The
inspection cell 10 retained by the cell carrier 50 by various
means. such as friction, constriction, adhesive or thread. The cell
carrier 50 has an upper opening 52 and a cylindrical upper void 54.
The void and the opening allow inspecting light to pass through the
inspection unit without an interruption. The interface 56 between
the upper planar surface of the inspection cell and the cell
carrier form a tight seal such that the carrier liquid does not
leak between the inspection cell 10 and the cell carrier 50.
Accordingly to the present invention, the upper opening 52 and the
upper void 54 of the carrier are larger than the opening of the
indentation of the inspection cell. When an amount of the carrier
liquid is placed in the inspection unit to allow the liquid to fill
the indentation and some portion of the upper void 54, a meniscus
58 is formed along the wall of the upper void 54. Because the upper
void 54 is larger than the opening of the indentation, the bent
peripheral edge of the meniscus is located outside of the field of
inspection, which is equal to or smaller than the diameter of the
opening of the indentation. Optionally, the bottom of the upper
void has an extended lip that is extended towards the axis of the
upper void cylinder such that the extended lip interrupts or blocks
the passage of the light outside the opening of the indentation of
the inspection cell. The interruption by the extended lip masks the
light from reaching the bent peripheral edge of the meniscus,
thereby eliminating the image distorting effect of the meniscus.
The extended lip feature of the cell carrier is more effective when
the carrier blocks the passage of light, i.e., the extended lip or
the whole cell carrier is opaque.
[0025] The cell carrier can be fabricated from a variety of solid
materials since the carrier only functions as a rigid material that
holds one or more of the inspection cells. Suitable materials
include various thermoplastic polymers, e.g., polyethylene,
polypropylene, polystyrene, polyester, polyamide, acrylic polymers
and the like; metals, e.g., aluminum, iron, brass, copper, and the
like; thermoset polymers; and the like. Preferably, suitable
materials for the cell carrier are opaque or translucent, since
such materials provide the above-described masking effect.
Additionally, an opaque or translucent material is preferred since
the surfaces of the carrier and the interfaces of the carrier and
the inspection cell may cause unwanted scattering of light if the
carrier is fabricated from a transparent or light-reflecting
material. Such unwanted scattering of light may interfere with the
proper lighting condition for the inspection cell. e.g., by making
the lighting condition uneven, or producing undesirable bright
spots and shadows. More preferred materials for the carrier are
opaque. e.g., gray or black, and most preferred are black. It is to
be noted although the cell carrier is illustrated above in
conjunction with a carrier that holds one inspection cell, the cell
carrier can be designed to hold more than one inspection cell such
that a multitude of inspection cells can be simultaneously conveyed
and inspected.
[0026] The inspection cell of the present invention is suitable for
manual and automated inspection systems. Exemplary suitable
automated inspection systems are disclosed in European Patent
Application No. 91810978.6, U.S. Pat. No. 5,574,554 and European
Patent Application No. 95304003.7.
[0027] The inspection cell of the present invention is highly
suitable for inspecting an article, especially a transparent or
translucent article, suspended or submerged in liquid. The
inspection cell of the present invention provides many advantages
over prior art inspection cells. For example, the inspection cell
allows the article to settle to the apex of the indentation such
that the location of the article in the cell is predictable, and
the inspection cell does not significantly distort the light
passing through the cell when the carrier liquid is placed in the
cell. The inspection cell is highly suitable for various inspection
systems, especially for machine inspection systems.
[0028] The present invention is further illustrated with the
following example. However, the example is not to be construed as
limiting the invention thereto.
EXAMPLE
[0029] A reusable inspection cell is produced from quartz. A
cylindrical quartz block, having a diameter of about 22.2 mm and a
length of about 8 mm and having two parallel planar surfaces, is
ground to have a hemispherical indentation of an about 11 mm
radius. The apex of the indentation is about 2 mm above the bottom
planar surface of the quartz cylinder. The indentation and the
lower planar surface of the quartz block are polished to have an
optical finish. The resulting inspection wetcell exhibits highly
uniform optical properties over the indentation and is highly
scratch resistant, making the wetcell highly suitable for
inspecting hydrogel contact lenses. The indentation is filled with
an isotonic sodium chloride saline solution, and a hydrogel contact
lens having a diameter of about 14 mm and a front curve radius of
about 9 mm is placed in the indentation. The hydrogel lens
consistently settles to the center of the indentation, and the high
scratch resistance of quartz makes the wetcell highly suitable for
many repeated use and wash cycles of the lens inspection
process.
* * * * *