U.S. patent application number 12/568010 was filed with the patent office on 2010-03-11 for method for manufacturing ophthalmic lenses using circular blanks.
This patent application is currently assigned to Essilor International (Compagnie Generale D'optique). Invention is credited to Walter Danhardt, Roland Mandler, Dan Riall, Marc Silva.
Application Number | 20100060848 12/568010 |
Document ID | / |
Family ID | 34201953 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100060848 |
Kind Code |
A1 |
Mandler; Roland ; et
al. |
March 11, 2010 |
Method For Manufacturing Ophthalmic Lenses Using Circular
Blanks
Abstract
For manufacturing ophthalmic lenses and other optical form
bodies made of plastic material, plastic form parts are used which
are made by non-cutting shaping and are then further worked by
mechanical production steps. Said plastic form parts are circular
blanks (1) made of two different plastic materials which are firmly
joined to each other. Thereby, an interior lens element (2) that
consists of a high-quality material is concentrically surrounded by
a ring fixture (3) which consists of a low priced material. Either
surface of the lens element (2) may feature any given geometry.
During mechanical working, the ring fixture (3) is used for
mounting as well as for depositing and, in addition, for
stabilizing the workpiece (9). For this reason it is partially
maintained throughout the mechanical working and is cut off at the
end only.
Inventors: |
Mandler; Roland;
(Heuchelheim, DE) ; Danhardt; Walter; (Roanoke,
VA) ; Riall; Dan; (Roanoke, VA) ; Silva;
Marc; (Roanoke, VA) |
Correspondence
Address: |
OCCHIUTI ROHLICEK & TSAO, LLP
10 FAWCETT STREET
CAMBRIDGE
MA
02138
US
|
Assignee: |
Essilor International (Compagnie
Generale D'optique)
Charenton Le Pont
FR
|
Family ID: |
34201953 |
Appl. No.: |
12/568010 |
Filed: |
September 28, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10569762 |
Mar 15, 2007 |
|
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PCT/IB2004/002721 |
Aug 20, 2004 |
|
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12568010 |
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Current U.S.
Class: |
351/159.01 |
Current CPC
Class: |
B24B 13/005 20130101;
B29D 11/00009 20130101; B29D 11/00942 20130101 |
Class at
Publication: |
351/159 |
International
Class: |
G02C 7/02 20060101
G02C007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2003 |
DE |
10338893.1 |
Claims
1-19. (canceled)
20. A circular blank for manufacturing ophthalmic lenses and other
form bodies made of plastic material, comprising a lens element
made of a high-quality optical material which is worked using
mechanical production steps, wherein the lens element is surrounded
by a ring fixture made of a low-cost material, wherein the lens
element and the ring fixture made of two different plastic
materials are firmly connected to each other, and wherein the ring
fixture is mountable in a mounting tool of a working machine and is
machinale together with the lens element.
21. The circular blank according to claim 20, wherein the ring
fixture has a recess for receiving the lens element.
22. The circular blank according to claim 21, wherein the recess is
provided with a flange to support the lens element.
23. The circular blank according to claim 20, wherein the ring
fixture has ribs, webs or the like with spaces (37) in-between.
24. The circular blank according to claim 23, wherein the ribs are
radially arranged.
25. The circular blank according to claim 20, wherein the periphery
of the ring fixture is provided with a collar.
26. The circular blank according to claim 20, wherein the ring
fixture is concentric to the lens element.
27. The circular blank according to claim 20, wherein the ring
fixture is an injection moulded part.
28. The circular blank according to claim 20, wherein the ring
fixture is bonded to the lens element, for example by an
adhesive.
29. The circular blank according to claim 20, wherein the ring
fixture includes at least one member for mechanical
registration.
30. The circular blank according to claim 20, wherein the ring
fixture is a handle.
31. A circular blank according to claim 20 for use in manufacturing
ophthalmic lenses and other form bodies made of plastic material
Description
[0001] The invention relates to a method for manufacturing
ophthalmic lenses, more commonly known as spectacle lenses. The
invention further relates to circular blanks for manufacturing
ophthalmic lenses and other form bodies made of plastic
material.
[0002] In any machining process, the fundamental process elements
are the cutting tool and the work holding fixture. In form
machining of plastic spectacle lenses, work holding is particularly
important because lenses are easily deformed when subjected to
external forces.
[0003] Therefore, the work holding method must basically [0004]
accurately locate the work piece, [0005] prevent any movement of
the work piece during machining and [0006] prevent any strain on
the work piece due to cutting and clamping forces.
[0007] It is well known to optimize the thickness of a spectacle
lens in order to minimize its weight. In this optimization process,
the thickness in the center of a plus powered lens is reduced
against the thickness remaining at the edge of the lens which must
fit a given lens frame. In case of minus powered lenses the
thickness in the center is reduced to a minimum irrespective of the
edge, just to ensure the mechanical stability of the lens.
[0008] This so-called thickness optimization causes the following
problems: [0009] During surface machining, the edge of the lens is
cut. Therefore, the outside diameter of the spectacle lens is
unsuited for clamping. [0010] Due to the various shapes and sizes
of the lens frames the edge of each lens after machining is not
circular any more. For further processing, special mounting devices
and manufacturing methods are required as well as a plurality of
different working tools. [0011] While the blank is machined, the
rigidity of each lens decreases due to the thickness optimization
and the used plastic material.
[0012] To ease these problems, DE-A1-40 03 002 for example
describes a blocking method for manufacturing spectacle lenses. A
block or handle is bonded to the lens surface using wax,
low-melting alloy or other removable adhesives. The block provides
the datums for accurately fixing the lens in a cutting machine. The
block is then clamped with sufficient pressure so as to resist any
cutting forces caused by machining.
[0013] This type of work holding has the following disadvantages:
[0014] It is difficult to accurately place the block according to
the optical characteristics of the lens. [0015] The optical surface
must be coated with a film for protection against the adhesive
(additional operation). [0016] The curing process (shrinkage) of
the adhesive material will cause deflection of the lens. [0017] The
block permits only machining of one side of the lens at a time.
[0018] The block and protective film must be removed from the lens
later (subsequent process).
[0019] Other methods propose radial clamping the lens on its
outside diameter (perphery), e.g. directly in a chucking device
that squeezes the lens blank. In this type of system, the lens
itself must provide the datums for accurate fixturing in the
cutting machine.
[0020] This type of work holding has the following disadvantages:
[0021] The pressure from the clamping chuck (needed to resist the
cutting forces) causes deformation of the work piece whereby the
optical properties are affected. [0022] Normal lens blanks are not
particularly suited for accurate datums. Normally, they are not
sufficiently round, nor have they some feature that could be used
for indexing. [0023] Since the lens blanks come in many different
sizes and shapes, direct radial clamping does not lend itself to
automation very well (robot tooling must work on many different
sizes and shapes of lens blanks). [0024] Plus powered lenses have
very thin edges which are--difficult to locate, to clamp and to
provide clearance for machining.
[0025] To remedy these deficiencies, US-A1-2003/0022610 describes a
method of manufacturing spectacle lenses using molded round blanks
having a diameter considerably larger than the diameter of the
spectacle lenses to be produced. Each blank is clamped on its
outside diameter and is machined on a first side, preferably on a
convex front side. Thereafter the semi-finished lens is cut out
from the lens blank approximately along its definite outer contour,
for example using a laser tool. The cut-out part is then joined,
with an axial offset, to the remaining edge portion which serves as
a ring fixture or a clamping portion for the subsequent machining
operations.
[0026] This type of work holding has the following disadvantages:
[0027] Cutting a semi-finished lens and controlling axial
displacement relative to the edge part with subsequent welding of
both components requires an elaborate and very expensive special
machine having laser devices. Due to the additional operations, the
production process becomes highly expensive, too. [0028] The
twofold cutting and the welding of both components result in
finished lenses that are under considerable permanent thermal
tension. Many of the plastic materials used, however, are quite
vulnerable to thermal tensions and react after some time, showing
crack initiation in the rim region. This is unacceptable and
constitutes a great disadvantage of the procedure. [0029] Another
shortcoming is that in cutting the finished lens, the edge portion
of the workpiece is scrapped as waste. Because expensive plastic
materials are required for the production of spectacle lenses, the
material expenditures are high.
[0030] It is an object of the present invention to provide a method
for manufacturing spectacle lenses within a work holding fixture
suited to prevent any strain on the work piece due to cutting and
clamping forces. It is another object of the invention to reduce
production cost.
[0031] Furthermore, the lens blank should be reproducible and
accurately placeable according to the optical characteristics of
the lens. No added operations, coatings for example, should be
required. The work fixture is to permit machining of both sides of
the lens at a time.
[0032] Main features of the invention are recited in claim 1 and in
claim 20. Specializations form the subject matter of claims 2 to 19
and of claims 21 to 30. Claim 31 refers to the use of a circular
blank.
[0033] According to the invention, the procedure for manufacturing
lens distinguishes over the prior art in that the plastic shaped
parts (circular blanks) consist of two different materials, one
high-quality material in the center and one less expensive material
in the rim region. The above mentioned increase in diameter is thus
created by means of an outer plastic ring made of less expensive
material.
[0034] For reasons of linguistic simplification in the following
context, plastic shaped parts are referred to as [plastic] circular
blanks. These may be blanks (both sides being without optical
quality) or semi-finished parts (one side having optical quality).
The plastic circular blanks can be finished ones without a
protruding structure at the rim, or they may include a shaped rim
that protrudes from the surface.
[0035] But in any, case the circular blanks are made of two
different plastic materials whereby the inner central region
consists of high-quality transparent plastic suitable for the
manufacture of a lens. This inner central region is hereinafter
referred to as lens element. This lens element is surrounded by a
plastic ring made of a less expensive plastic material and is
hereinafter referred to as ring fixture.
[0036] This ring fixture is tightly joined to the lens element so
that together, they compose the plastic circular blank. The ring
fixture serves as a handle for mounting and depositing of the
circular blanks during the manufacturing process for the spectacle
lenses. Thus, it is also possible to provide for optimization of
thickness during the manufacture without having to cope with the
above-mentioned problems in the rim region. The ring fixture is
detached, together with a narrow region of the lens element of the
finished work, at the end of all important production steps
only.
[0037] It is advantageous that the waste predominantly consists of
low cost material and that available forms can be used for
manufacturing the lens elements since they have the same diameters
as is customary for the blocking-on-procedures. However, provision
is also made for other diameters. Non-cutting shaping procedures
comprise inter alia these: casting, injection molding, pressing,
bonding and welding. Cutting shaping is meant to include inter alia
the following procedures: milling, lathing, grinding, fine
grinding, polishing and engraving. In the case of manufacturing
plastic circular blanks, the lens element is produced first,
preferably with non-cutting shaping procedures like casting or
injection molding. Available forms previously manufactured in
connection with other production processes are used as far as
possible.
[0038] Next, the ring fixture is manufactured and connected to the
lens element during the process or thereafter. There are
several-possibilities for these production steps: [0039] 1. The
lens element is put into a suitable form whose diameter is
definitely larger than that of the lens element and the ring
fixture is cast around it. To this end, casting procedures are
considered for which fluid hardening plastics are used, or
injection molding is applied by which the plastic material is
plasticized under heat supply and is injected under pressure around
the lens element With these procedures, a subsequent joining of
both elements can be omitted because the ring fixture is already
tightly fixed to the lens element during the manufacturing process.
[0040] 2 The ring fixture is manufactured as a separate element
using one of several procedures such as casting, injection molding,
cutting from a hollow cylinder or the like. The ring fixture made
in such a way is then connected to the lens element. Again there
are several possibilities for doing this such as bonding laser
welding, ultrasonic welding, etc. Any changes thereby possibly
created in the rim region of the lens element are unimportant,
because when afterwards the ring fixture is cut off from the
finished lens, the cutting occurs within the high-quality material
and the joint region is dropped out. If a small part of the
high-quality material of the lens element is also cut out, that
will only be an insignificantly small amount of material.
[0041] Regarding the shaping of the lens element and of the ring
fixture as well as the following working on the plastic circular
blank, there are again several versions.
Version I:
[0042] For the non-cutting shaping of the lens element, there are
the following possibilities for the design of both surfaces: two
coplanar plane faces, a plane face and a roughly pre-shaped face,
two roughly pre-shaped faces, as well as a plane face or a roughly
pre-shaped face combined with a second face having optical quality.
In this case, the rim of the lens element also includes a cast-on
marking by which the axis of the finished lens side is defined.
[0043] If the lens element of the circular blank comprises already
a pre-shaped surface of optical quality prior to the mechanical
working to obtain the second lens surface, its shape is calculated
in such a way that the effects of both surfaces are added to the
desired optical properties of the finished lens. Thus the number of
required forms for manufacturing lens elements, one side of which
is of optical quality, can be reduced considerably. This allows for
larger jumps of diopter which are interpolated as the second side
of the lens is worked. The same advantage is also achieved with the
versions of the procedures IIA and IIB (see below).
[0044] The ring fixture is shaped like a shallow hollow cylinder
and is of similar height as the lens element. Both parts are joined
to one another and compose the plastic circular blank.
[0045] In the course of the following working steps including
optimization of thickness, the circular blank is mounted at the
outer rim and the lens body is worked by means of cutting
procedures (milling, lathing, grinding, polishing). The working
tools are used in such a way that an outer annular region of the
circular blank maintains an almost unchanged thickness. To this
end, the working tools are started from the center and continue
along the contour of the lens to be manufactured whereupon they
move backwards again in the rim region of the workpiece (worked-on
plastic circular blank) so that the outer annular region mentioned
is worked. However, the mechanical working may also begin in the
rim region and move on to the center.
[0046] During the entire manufacturing process, this annular region
is available for mounting and depositing the workpiece. Due to the
annular region, mechanical stability of the manufactured lens is
assured, too, which is a great advantage in view of the high
working pressures caused by the tools. An unallowable deformation
of the lens element caused by the cutting forces will not take
place due to the supporting function of the annular region.
[0047] Owing to the greater diameter of the plastic circular blank
and the special mode of controlling the working tool, it can be
avoided to unduly cut the outer periphery of the workpiece in the
course of optimizing the thickness during the mechanical working,
whereby mounting at the outer periphery rim would become
impossible.
[0048] At the end of all working steps, i.e. following the coating
and marking, the actual lens is cut out of the center of the
workpiece. The annular region and shaped rim, respectively, of the
workpiece is mounted to the workpiece spindle of a milling machine,
and the inner contour of the lens is cut by means of an end mill of
small diameter. Other procedures may also be employed for cutting
out. For example, a waterjet or a laser may be used.
[0049] The contour of the section rim can (with machining
allowances) completely or roughly conform with the shape of a lens
frame although other contours are possible, too, e.g. a circle
form. Cutting is carried out at the rim region of the lens element
in order that the connective portion between the lens element and
the ring fixture is cut off the lens body in any case.
[0050] Because the ring fixture is made of another kind of plastic,
the cut material of the rim region and the produced piece of waste
consists chiefly of that cheaper material and only a very small
portion is of the high-quality lens material. The result is
substantial economy regarding material costs. Further savings are
obtained with procuring working tools since casting molds on hand
with most of the manufacturers can be used for the manufacturing of
the lens element.
Version II:
[0051] The lens element is always manufactured in such a manner
that a plane face or a roughly pre-shaped face is combined with a
second face already provided with optical quality. A marking is
also provided on the lens element for defining the axis of the lens
side which is finished by the casting process. Here, the ring
fixture is ring-shaped such that the cross-sectional areas are of
rectangular or trapezoidal shapes. However, other cross-sectional
forms are also envisaged. The two parts (lens element and ring
fixture) are joined to one another and together they compose the
circular blank including the shaped rim in such a manner that the
ring fixture protrudes at that side beyond the lens element which
has the optical quality surface. So it constitutes the shaped rim
there. Since this side of the plastic circular blank will not have
to be worked any more, the protruding fixture or shaped rim will
not impede further working. The other side of the plastic circular
blank (plane or roughly pre-shaped) can be worked up to the rim
region without obstructions, since mounting is effected via the
shaped rim at the other side of the plastic circular blank.
[0052] If the concave rear side of the lens element is of optical
quality and the shaped rim is protruding there, version IIA is
concerned. On the other hand, if the convex front side of the lens
element is of optical quality and the shaped rim is protruding
there, version IIB is concerned.
[0053] During the following working steps comprising thickness
optimization, the plastic circular blank outer portion (periphery)
is mounted via the shaped rim and that side of the lens is worked
which still lacks optical quality. To this end, cutting procedures
(milling, lathing, grinding, polishing) are applied with the
working tools being particularly easy to operate because there are
no limitations to their movements which might be caused by the
design of the workpiece. Thus it is also possible and
technologically advantageous to move the working tools (if
reasonable) beyond the rim of the workpiece.
[0054] During the cutting procedure, this shaped rim is
substantially maintained and it is available at all working steps
for mounting and depositing of the workpiece. A stabilization of
the manufactured lens is also achieved by the shaped rim which is
again a great advantage in view of the high working pressures
caused by the working tools. An unallowable deformation of the lens
element caused by the cutting forces is prevented by the supporting
function of the shaped rim.
[0055] The larger diameter of the plastic circular blank and the
available shaped rim ensure that during the mechanical working, the
outer periphery the workpiece will lose height only to a minor
extent within the optimization of thickness. Enough material will
remain at the rim region for mounting at the outer periphery or
shaped rim.
[0056] At the end of all working steps, the actual lens body is cut
out of the center of the workpiece, as already mentioned with
reference to version I. The same advantages of material and working
tool cost savings result.
[0057] Conventional casting and injection molding machines and
working tools can be used for effecting the procedures according to
versions I and II. The techniques required for connecting the lens
element and the ring fixture are available as well. Likewise,
conventional working machine and tools can be employed for cutting
and polishing the workpieces.
[0058] CNC-controlled machines and the appropriate special working
tools are beneficial for cutting and polishing according to
versions I and IIA. As to version IIB, simpler working machines may
be used.
[0059] Further features, details and advantages of the invention
will be evident from the wording of the claims and from the
following description of embodiments with reference to the drawings
wherein:
[0060] FIGS. 1a to 1c show different plastic circular blanks,
[0061] FIGS. 2a to 2c show the circular blanks of FIG. 1a to 1c and
their further processing,
[0062] FIGS. 3a and 3b show other embodiments of circular
blanks,
[0063] FIGS. 4a and 4b show the circular blanks of FIGS. 3a and 3b
and their further processing,
[0064] FIGS. 5a and 5b show further embodiments of circular
blanks,
[0065] FIGS. 6a and 6b show the circular blanks of FIGS. 5a and 5b
and their further processing,
[0066] FIG. 7 shows another embodiment of a circular blank.
[0067] FIGS. 8 a to 8c show the circular blank of FIG. 7 and its
further processing and
[0068] FIGS. 9a and 9b show yet another embodiment of the
invention.
[0069] FIGS. 1a to 1c illustrate three different embodiments of
plastic circular blanks 1, as manufactured by non-cutting shaping
procedures. FIGS. 2a to 2c show schematically the manufacturing
process.
[0070] FIG. 1a concernes a circular blank 1 having a lens element 2
that consists of a plane cylinder, with the front and rear sides
comprising a plane face 5 each. This lens element 2 is made of a
high-quality transparent plastic material having a high refraction
index, which is suitable for the manufacturing of spectacle lenses
and is accordingly expensive. The lens element 2 is manufactured by
non-cutting shaping procedures such as casting, injection molding,
pressing, etc.
[0071] A ring fixture 3 has the shape of a plane hollow-cylinder
whose cross-section forms rectangles. Its height corresponds to the
height of the lens elements 2. It consists of a cheap plastic
having properties which match those of the lens element 2 so that
joining these components is possible without problems. Although the
ring fixture 3 can be manufactured by non-cutting shaping, it is
also possible to cut it off a precast hollow cylinder plastic tube
so that large quantities of these ring fixtures 3 can be produced
in rapid sequences.
[0072] The finished ring fixture 3 is then joined to the lens
element 2 whereby the circular blank 1 is created. For such
bonding, adhesive processes are considered using liquid plastic,
which are hardened e.g. by means of ultraviolet light or an added
hardener. However, welding procedures are also contemplated with
the heat required being supplied, for example, by laser or
ultrasound technologies. Other welding procedures may be used,
too.
[0073] Moreover, it is provided that the lens element 2 is put into
a form and the ring fixture 3 is Molded around the lens element 2
by casting or injection molding procedures. Since in this case the
material of the ring fixture 3 is liquid, especially as a liquid
plastic or heated thermoplastic material, this casting procedure
will bring about solid adhesion between the lens element 2 and the
ring fixture 3.
[0074] FIG. 1b concernes a circular blank 1 with a lens element 2
one side of which is already pre-shaped into a concave surface 4 by
non-cutting shaping. The concave surface 4 may be roughly
pre-shaped or may be a surface of optical quality which already
forms the concave rear side of the lens. The other side of the
plastic circular blank 1 consists of a plane face 5. Manufacture of
the ring fixture 3, choice of materials and production processes
are the same as already explained with reference to FIG. 1a.
[0075] FIG. 1c shows a circular blank 1 with a lens element 2 both
sides of which have already been pre-formed as a concave surface 4
and as a convex surface 6, respectively, by non-cutting shaping
procedures. These may be roughly pre-shaped surfaces or it may be
provided that one of the two surfaces, preferably the concave
surface, is already of optical quality and thus is the already
finished side of the lens. Manufacture of the ring fixture 3,
choice of material and production processes are the same as
explained above with reference to FIG. 1a.
[0076] FIG. 2a illustrates how a circular blank 1 shaped according
to FIG. 1b is put into a mounting tool 7 fixed to a workpiece
spindle 8 of a machine tool (not shown). The concave surface 4 of
optical quality is made by means of a conventional milling,
lathing, grinding and polishing procedure, with the ring fixture 3
only slightly cut. The concave surface 4 of the lens element 2 is
the finished rear side of the spectacle lens 12.
[0077] Since the designation plastic circular blank 1 strictly
speaking applies only to an unworked component, the pre-worked
plastic circular blank 1 is hereinafter also termed workpiece
9.
[0078] According to FIG. 2b, the workpiece 9 has been flipped by
180.degree. and inserted again into the same mounting tool 7. The
concave surface 4 of optical quality points now towards the
mounting tool 7 which again is fixed to the workpiece spindle 8 of
a machine tool. By the cutting procedures mentioned, the convex
surface 11 was manufactured in optical quality whereby the region
of the lens element 2 already is the finished front side of the
spectacle lens 12.
[0079] By appropriate operating the working tool, the annular
region 10 was pre-worked, so as to serve during the following
working steps for mounting and depositing. It chiefly consists of
the cheaper material of the ring fixture 3. This annular region 10
also serves as a support of the working piece 9 in the thin rim
region.
[0080] The annular region 10 could be manufactured only by moving
the working tools upwards in the rim region of the workpiece 9
whereby the tools were prevented from cutting into the outer
periphery of the workpiece 9 and possibly of the mounting tool 7 as
well. This would have happened if the working tools had continued
to follow the contour of the convex surface 11.
[0081] The annular region 10 consists mainly of the cheap material
of the ring fixture 3 and only to a minor part of the high-quality
material of the lens element 2.
[0082] Later on, separation of the actual lens 12 from the annular
region 10 is effected along a contour which is marked by two
section lines 13 in the sectional view. This contour corresponds to
the provided lens frame either exactly or with a size allowance so
that the optician can adapt it.
[0083] In FIG. 2c, the lens 12 and annular region 10 are seen as
already separated from one another along a contour which, according
to the section lines 13, is given by the shape of a lens frame.
[0084] The lens 12 consists entirely of the high-quality material,
whereas the waste portion 18 consists mainly of the cheaper
material of the ring fixture 3 and only to a minor part of the
narrow rim region 15 of the lens element 2. This results in
considerable material savings.
[0085] Since for separating the lens 12 from the workpiece 9, the
cut is completely carried out within the material of the lens
element 2, the joint 14 is located between that and the ring
fixture 3 in the waste portion 18. Therefore, this interference
zone cannot affect the spectacle lens 12.
[0086] The advantage of this version I of the procedure is that
both sides can be worked on and thus spectacle lenses 12 can be
made with whatever shape according to prescription. Storage
expenses are relatively low, too, because few plastic circular
blanks 1 with finished surface have to be stored. Besides, material
costs are lower due to the rim region being of less expensive
material, and further savings result from the fact that available
form tools can be used.
[0087] In FIGS. 3a and 3b illustrates two different embodiments of
the circular blank 1 made by means of non-cutting shaping. FIGS. 4a
and 4b show schematic manufacturing sequences.
[0088] Inter alia, FIG. 3 show two different embodiments of the
plastic circular blanks having shaped rims 16, made by non-cutting
shaping. In this version IIA, the concave surface 4 must at any
rate have been provided with optical quality already because it is
not accessible any more for mechanical working.
[0089] FIG. 2a illustrates a plastic circular blank 1 having a
shaped rim 16 formed by the ring fixture 3. The shaped rim 16
considerably protrudes beyond the lens element 2, which has
production related advantages during the cutting procedure. To one
side of the lens element 2, a concave surface 4 of optical quality
has to be pre-formed because, as mentioned, it is not freely
accessible for mechanical working due to the protruding shaped rim
16.
[0090] This concave surface 4 already is the finished rear side of
the lens 12. The other side of the lens element 2 comprises a plane
face 5. It is seen that the shaped rim 16 formed by the ring
fixture 3 is slightly displaced downwards, together with its top
side 17, relative to the plane face 5. Other embodiments are also
contemplated in which the top side 17 and the plane face 5 are in
one plane.
[0091] Manufacture of the ring fixture 3, the choice of material
and the manufacturing techniques are the same as already mentioned
with reference to FIG. 1a.
[0092] FIG. 3b shows a plastic circular blank 1 having a shaped rim
16 with a lens element 2 of which both sides have already been
pre-formed by way of a concave surface 4 and a convex surface 6,
respectively, through non-cutting shaping.
[0093] The convex surface 6 is a roughly pre-shaped face which
still has to be mechanically worked. The concave surface 4,
however, must at any rate already have optical quality, created by
non-cutting shaping. This is necessary because the concave surface
4 is not accessible any more for mechanical working due to the
protruding shaped rim 16.
[0094] Referring to FIG. 3b, the top side 17 of the shaped rim 16
formed by the ring fixture 3, is again slightly displaced downwards
relative to the convex surface 6. However, other embodiments are
also contemplated.
[0095] Manufacture of the ring fixture 3, the choice of material
and of the manufacturing techniques are the same as mentioned above
with reference to FIGS. 1a to 1c.
[0096] FIG. 4a shows a workpiece 9 which originated from the
originally shaped plastic circular blank 1 according to FIG. 3b by
mechanical working. The workpiece 9 is inserted into a mounting
tool 7 connected to a workpiece spindle 8 of a machine tool (not
illustrated). The convex surface 6 was manufactured with optical
quality by a conventional procedure such as milling, lathing,
grinding and polishing, the shaped rim 16 formed by the ring
fixture 3 being cut only slightly. The convex surface 6 of the lens
element 2 comprises the finished front side of the lens 12. Thus
both surfaces of the lens 12 are of optical quality.
[0097] Later on, separation of the actual lens 12 off the shaped
rim 16 is effected along a contour which is marked by two the
section-lines 13 in the sectional view of FIG. 4a. This contour
corresponds to the provided lens frame either exactly or with a
size allowance, for adaptation by an optician.
[0098] FIG. 4b shows the lens 12 already cut off from the workpiece
9 along a contour according to the section boundaries 13 given by
the shape of a lens frame.
[0099] The lens 12 consists entirely of high-quality material
whereas the waste portion 18 is formed by the narrow rim region 15
of the lens element 2 and the ring fixture 3. Thus the waste 18 is
made up chiefly of the cost-effective material of the ring fixture
3 and only to a small part of the material of the lens element 2.
Considerable material expenditures will be saved in this way.
[0100] Since the cut separating the lens 12 out of the workpiece 9
runs completely within the material of the lens element 2, the
joint 14 is located between this and the ring fixture 3 or the
shaped rim 16, respectively, in the waste portion 18. This
interference zone cannot affect the lens 12.
[0101] The advantage of this procedure version IIA is that the
convex surface 6 is very easily accessible for mechanical working
whereby production cost is saved. Besides material costs are lower
because the rim region is made of cheaper material. Other savings
result from the fact that available form tools can be used with the
machine tools.
[0102] In FIGS. 5a and 5b, two different embodiments are
illustrated of the circular blank 1 made by non-cutting shaping.
FIGS. 6a and 6b show a schematic manufacturing sequence.
[0103] Inter alia, FIG. 5 shows two different embodiments made by
non-cutting shaping of the plastic circular blanks having shaped
rims 16. In this version IIB, the convex surface 6 must be made
with optical quality already because it is not freely accessible
any more for mechanical working.
[0104] FIG. 5a shows a plastic circular blank 1 having a shaped rim
16 surrounding the lens element 2 and formed by the ring fixture 3.
The one side of the lens element 2 has a convex surface 6 while the
other side is formed by a plane face 5.
[0105] Referring to FIG. 5a, the top side 17 of the shaped rim 16
is slightly displaced downwards relative to the plane face 5 in
view of production relevant reasons (less cutting scrap).
[0106] Other embodiments are also contemplated wherein the top side
17 and the plane face 5 are in one plane. The shaped rim 16
protrudes considerably beyond the lens element 2 at the side of the
convex surface 6, which also brings about advantages in the cutting
procedure.
[0107] As mentioned, the lens element 2, pre-formed by non-cutting
shaping, already has on one side a convex surface 6 which in this
case already must have optical quality because due to the
protruding shaped rim 16, it is not freely accessible for
mechanical working any more. Thus this convex surface 6 already
presents the finished front side of the lens 12. Concerning the
manufacture of the ring fixture 3, the choice of material and of
the production techniques, the statements mentioned with reference
to FIGS. 1a to 1c apply here as well.
[0108] FIG. 5b also illustrates a plastic circular blank 1 having a
shaped rim 16 with both sides being already pre-worked by
non-cutting shaping to yield a concave surface 4 and a convex
surface 6, respectively.
[0109] Referring to FIG. 5b, the top side 17 the shaped rim 16
formed by the ring fixture 3 is again displaced slightly downwards
relative to the concave surface 4 for production relevant reasons.
However, other embodiments are also contemplated. The shaped rim 16
protrudes considerably beyond the lens element 2 at the convex
side, resulting in production advantages with the cutting
procedure.
[0110] The concave surface 4 is a roughly pre-shaped face which
still has to be worked mechanically. However, the convex surface 6
produced by non-cutting shaping must already be of optical quality
at any rate because due to the protruding shaped rim 16, there is
no free access for working any more. Again for the manufacture of
the ring fixture 3, the choice of material and of the manufacturing
techniques, the same applies as already mentioned with reference to
FIGS. 1a to 1c.
[0111] FIG. 6a illustrates a workpiece 9 which was formed from a
circular blank 1 originally shaped according to FIG. 5b by
mechanical working the concave surface 4. The workpiece 9 is put
into the mounting tool 7 connected to the workpiece spindle 8 of a
working machine (not shown).
[0112] The concave surface 4 is manufactured with optical quality
by a convention procedure such as milling, lathing, grinding and
polishing, the shaped rim 16 formed by the ring fixture 3 being cut
only slightly. The concave surface 4 of the lens element 2 presents
the finished rear side of the lens 12 whose surfaces, therefore are
both available in optical quality.
[0113] The separation of the actual lens 12 off the workpiece 9
occurs later on along a contour marked by two section lines 13 in
the views of FIGS. 6a and 6b. This contour corresponds to a given
lens frame either exactly or with a size allowance so that the
optician can adapt it.
[0114] FIG. 6b shows the lens 12 as already separated from the
workpiece 9 by cutting along a contour according to the section
boundaries 13 determined by the shape of a lens frame.
[0115] The lens 12 consists entirely of high-quality material,
whereas the waste portion 18 is formed by the narrow rim region 15
of the lens element 2 and the ring fixture 3 or the shaped rim 16,
respectively. For this reason, the waste part 18 consists chiefly
of the cheaper material of the ring fixture 3, and only to a small
part of the material of the lens element 2, whereby considerable
material expenditures are saved.
[0116] Since the cut for separating the lens 12 from the workpiece
9 was completely carried out within the material of the lens
element 2, the joint 14 is located between this and the ring
fixture 3 in the waste portion 18 so that this interference zone
cannot affect the lens 12.
[0117] The advantage of the procedure as per version IIB is that
the concave surface 4 is very easily accessible for mechanical
working, resulting in production economy and also in less material
costs (rim region is made of less expensive material). Other
savings come about by the working tools, as available shaping tools
can be used.
[0118] FIG. 7 shows another embodiment of a circular blank 1
according to the invention including a lens element 2 and a ring
fixture 30 having a recess 32 that forms a flange 34 near the
bottom which supports the lens element 2 inserted into the ring
fixture 30. It is bonded to the outer diameter (periphery) 26 of
the lens element 2 by an adhesive and is made of a low-cost plastic
material adapted to be readily machined in the lens making process,
without damage to tools or contamination to swarf.
[0119] The function of the flange 34 is to simplify the assembly
process, setting the height of the lens element 2 relative to the
body of the ring fixture 30. If the flange 34 were not there, the
height would have to be set by a fixture of some sort. Putting the
flange 34 into the ring fixture 30 eliminates the need for separate
fixturing.
[0120] As shown in FIG. 7, the ring fixture 30 may be provided with
radial ribs 36 and spaces 37 in-between. These ribs 36 are intended
to save material volume without sacrificing component part strength
and stability during the machining and polishing processes. Using
an injection molding process, the ring part 30 can be manufactured
at low cost.
[0121] The bottom of the ring fixture 30 has at its outer diameter
16 a collar 38 designed to allow the circular blank 1 to be gripped
and clamped at the various workstations. The collar 38 is bordered
by a flat annular abutment rim 39 (of given datum A) allowing
stable and accurate seating of the circular blank 1 against a
suitable support or mounting tool 7 of the workstation. The
abutment rim is in a preferred embodiment perpendicular to the
outer diameter 35 (of given datum B) of the collar 38 which is
coaxial to the axis L of the circular blank 1.
[0122] In an further embodiment, the ring fixture 30 and/or the
collar 38 comprises two or more diametrically opposed members (not
shown) for mechanical registration (of given datums) which are
separated from each other by at least one of their dimensions. This
will increase the accuracy and reliability of alignment.
[0123] In a first step--illustrated in FIG. 8a--the lens element 2
is inserted into the ring fixture 30. The joint 14 between the lens
2 and the ring 30 is filled up with an adhesive, no precision being
required for this assembly. The lens element 2 need not have
particularly good features or a circular outside diameter. After
curing, the lens element 2 assumes the accurate datums A, B of the
ring fixture 30.
[0124] The circular blank 1 is loaded into the cutting machine,
locating off the ring fixture datums and is clamped either radially
on the outer diameter 16 of the ring 30 or clamped axially. The
forces of clamping are not transmitted to the lens element 2, i.e.
no stress will occur. The first surface 11 is then machined.
[0125] After first surface machining (see FIG. 8b), some of the
ring fixture 30 will be consumed due to the size of the cutting
tool. Enough of the ring 30 remains, however, to support the lens
element 2 during subsequent operations. Next, the workpiece 9 is
flipped over, re-fixtured using the same datums A, B, and is
clamped as before. The second side is machined as shown in FIG.
8c.
[0126] After the second surface of the lens 2 is cut, more of the
ring fixture 30 will be consumed. Depending on the frame geometry
and the lens, some small portions of the ring 30 may be cut through
completely. Still, enough remains to prevent any strain on the lens
element 2 due to clamping forces or tool forces.
[0127] Alternatively, the ring fixture 30 may include accurate
datums A, B as part of its design, or it is mounted into a rigid
pallet 40 (see FIGS. 9a, 9b) that has its own accurate datums C and
is reusable. The ring fixture 30 will be mounted to the rigid
pallet 40 using mechanical means (not shown) and utilize the
pallet's datums C for cutting both front and back optical
surfaces.
[0128] The work holding methods described above have the following
benefits: [0129] precise datum features for accurate fixturing;
[0130] allow for machining both sides of the lens (convex and
concave) referencing off the same datum set--no remounting
required; [0131] the ring fixture 30 absorbs the clamping forces
from the machine's chucking system, preventing deformation of the
lens; [0132] allow for thin edges and non round lens shapes to be
cut; [0133] no precision is required at the bonding step since both
surfaces will be machined using the datums provided by the ring
fixture 30, particularly by the collar 38; [0134] the deformation
caused by bonding (shrinkage) is negligible because it is uniform
around the outer diameter of the lens element 2, not on the lens
surface; [0135] no surface protection is required on the lens
element 2; [0136] the outer diameter of the ring fixture 30 can be
more readily fixtured than a blocking lens which is beneficial for
automation and for downstream processes such as marking, cleaning,
coating, curing and inspection; [0137] the ring fixture 30 can be
cut as part of the machining process, allowing for thinner edge
geometry and non round shapes; [0138] after removal from cutting
machine, the datums are still part of the lens assembly (circular
blank 1) which is valuable for downstream processes.
[0139] In addition to the items above, there is an advantage in
optical material waste. With the outside diameter chucking, the
initial size of the lens blank 1 must be larger than the finished
lens size to provide sufficient chuck clearance. The lens 12 cannot
be cut all the way to the edge, nor can it be cut to a minimum edge
thickness without interfering with the chuck.
[0140] Using the ring fixture 30 permits reduction of both blank
diameter and thickness for production of same size finished lenses.
This translates into less waste of high cost optical lens
material.
[0141] All and any features and advantages--including design
details, spatial arrangements and procedural steps--arising from
the claims, the description and/or the drawings may be inventively
important both per se and in most variegated combinations.
TABLE-US-00001 List of Reference Symbols 1 plastic circular blank 2
lens element 3 ring fixture/handle 4 concave surface 5 plane face 6
convex surface 7 mounting tool 8 workpiece spindle 9 workpiece 10
annular region 11 convex surface 12 spectacle lens 13 section line
14 joint 15 narrow rim region 16 shaped rim/periphery 17 top side
18 waste portion 26 outer diameter/periphery 30 ring fixture/handle
32 recess 34 flange 35 outer diameter 36 rib 37 space 38 collar 39
abutment rim 40 pallet
* * * * *