Note: Descriptions are shown in the official language in which they were submitted.
-` 10~4~33~
MUI.TIFOCAL LENSES ANl) METHOD OF MAK NG SAME
BACKGROUND OF THE INVENTIOI~
Field of the Lnvention:
This invention relates to the manufacture of multlfocal
lenses and has particular reference to multifocal lenses formed
of laminates of thermoplastic lens materials and method of
making the same.
Description of the Prior Art:
In a conventional method of manufacturing multifocal
lenses, a lens segment consisting of one or more components of
high refractive index glass is fused onto the front or rear
face of a low refractive index major which is usually meniscus
in shape. The surface area of the ma~or where fusion takes
place mus~ be of optical quality meeting specific curvature,
smoothness, and cleanliness requirements. In addition, the sur-
face of the high refractive index segment must be of similar
optical quality in the area where it is to be fused onto the
ma~or. This requirement for two or more individual pieces for
each lens which includes the aforesaid preparation of all sur-
faces to be ~oined by fusion renders the method time-consuming,
subject to high scrap yield and costly.
Attempts to overcome at least some oE the costliness in
time, labor and inventory involved in grinding, polishing and
storing two or more glass pieces for each multifocal lens, the
prior art has cast lens blank segment portions directly into pre-
formed countersinks of lens major portions. This, however, has
the serious limitation of the multifocal segment in each case
having to consist entirely of a single refractive index glass
and be completely circular. U.S. Patent 2,992,518 is exemplary
of this technique.
~v~ '
dbl '
`` ~.0~3~
' Other prlor a~t practlces have involved the eas~lng and
pressing together of ma~or and minor pieces of glass, one being
rigid and the other caused to flow thereover. This technique,
in general, is exemplified in U.S. Patents Mos. 2,026,606;
2,433,013; and 3,149,948. It has, however, been larg'ely a-
bandoned in favor oE the first mentioned two-piece grinding,
polish-ing and mechanical assembly operations. Excessive dis-
tortion of interfaces between major and segment portions,
. bubbles, straw, fusing waves and cracking defects have tended
to render the end products inferior and largely commercially
unacceptable.
It has also been proposed heretofore to overcome the
' aforesaid difficulties by either casting a ma~or piece of glass
; over a rigid segment portion oE hi~her refractlve index or by
impressing the rigid segment into a viscous major portion of
relatively low refractive index glass.
Multifocal lenses prepared according to any one of the
aforementioned methods consist of a large area for distance,
vision and a relatively small portion for near vision.
To increase the size of the near vision portion of a
multiocal ophthalmic lens, raised ledge one-piece multi-
focals are now in use. In such lenses which are commonly re-
ferred to as Franklin multifocals, the near vision or "reading
portion" is prepared from a low refractive index blank by grinding '
the lower portion of the front surface of the lens blank to a
shorter radius of curvature. This produces a raised ledge be-
tween lower and upper parts of the front surface of the lens and,
in most cases, this raised ledge extends straight across from
; edge-to-edge of the lens.
Production of these one-piece raised ledge multlfocal
lenses requires the use of special and costly lens processing
equipment. Furthermore, lenses prepared according to processes
,. .
db¦ '
93
currently in use require a greater than usual cen~er thickness
to assure that their lmpact resistance meets present day re-
quirements after air hardening or ion exchange hardening. In
addition to lts tendency to weaken the lenses, the e~posed
raised ledge may be annoylngly reflective to light and collective
to dust and other contaminants.
While some of the difficulties experienced with the
raised ledge type of multifocal lenses may be overcome by cement-
ing or fusing two half-lens segments of different refractive in-
dices together in edge-to-edge relationship and grinding con-
tinaous object and ocular surfaces over the fused combination of
segments, other disadvantages arise. For example, there is the
main disadvantage of limitatlon of the lenses to s~lr~ace curva-
tures providing strong po~lers only and the need for extremely
wide variations of higfi and low refractive index glasses, beyond
those normally commercially available, to achieve combinations
of distance vision and reading portion powers normally required
in the field.
In addition to the foregoing drawbacks of prior art
multifocal lens manufacturing techniques, which to this point
have not dealt with matters of the so~called "progressive power
lens", there are the current problems of efficiently economi-
cally and reliably manufacturing the progressive power lens.
Progressive power lenses have one or more surfaces
whlch gradually change in their radii of curvature from center-
to-edge to provide a progressive change in refractive power of
the lens. ~eretofore the manufacture of these lenses required
complicated and excessively costly manufacturing procedures and
equipment9 notwithstanding the need for exceptional skill of
the artisan. They were either mechanically or manually surface
generated with lengthy, tedioos and costly multiple grinding and
db/
-` ~0~93~
regrinding operations or cast of plastic in molds having a
negative casting surface of the a3pheric curvature desired. In
the latter case, the negative aspheric surface of the mold it-
self required the practice of tedious, lengthy and diEficult
generating procedures for its preparation. Furthermore, when
completed, such a castlng surface can only produce a limited
number of good castings before being rendered unsuitable for
further use by scratching, cracking, chipping or general wear.
In view of the aforesaid drawbacks and related prob-
lems or difficulties of prior art multifocal lens manufacturingprocesses, it is a principle object of this invention to provide
8 novel
db/
L93~
simple and efficient method for producing improved mul~i-
focal lenses of various preselected types, all of laminated
blanks having the same simple basic geometry and which are
adaptable to being worked by conventional, simple single
vision lens tools and apparatuses requiring only ordinary
skills to operate.
SUM~RY OF THE INVENTION
The present invention relates to a method of making
a multifocal lens comprising the steps of: laminating a
layer of ophthalmic lens material of high refractive index
to a layer of ophthalmic lens material of a relatively low
refractive index to produce a high-low refractive index
interface theretween; shaping at least a portion of the
: laminate of the la~ers into the configuration of a yenerally
meniscus lens blank havinq the interface of the laminate
extending over a major portion of the blank diagonally ~rom
adjacent one side thereof to a point adjacent the opposite
'- side of the blank and corresponding meniscusly shapea;
-~ : grinding opposite sides of the blank to radii of curvature
desired of convex object and concave ocular surfaces of the
multifocal lens to be formed, the grinding at each side of
the blank being continued to a depth and in a a~ rection there-
into toward the interface according to a proximlty and orien-
tation required of the object and ocular surfaces of the lens
relative to the interface and to each other fo~ accomplishing
desired multiple focusing properties of the lens; and
polishing the thus ground surface.
In its apparatus aspect the invention relates to a
multifocal lens having convex and concavely curved opposite
~ sides, the lens comprising: a laminate of layers of high
and relatively low refractive index materials, the laminate
having a cupped high-low refractive index interace e~tending
B ~ 6 -
jb/~
~ 3V
diagonally from adjacent one of the lens sides to another
over a major portion o~ the lens, th~ in er~ace reaching
the immediate proximity of both the convex and concave lens
sides at least at one point on each; and the convex and
;; concave sides being of uninterrupted curvature from edge-
to-edge and polished.
The basic element used for producing blanks for
multifocal lenses according to this invention is a laminate
comprised of a layer of high refractive index material fused
or cemented onto a layer of lower re~ractive index material.
When, for example, oxide glasses are used as the thermoplas-
tic materials, fusion is preferred over cementinCJ. Layers
of the laminate are punched, cut or otherwise formed to
disc-like shapes prior to their lamination or suhsequent
thereto as a unit. In either case, flat blanks are formed
from which the multifocal lenses are produced. ~he blanks
are slumpe~, pressed or otherwise shaped to spherically or
..
aspherically meniscus configurations so as to similarly
shape, in eaah case, their high-low refractive index inter-
~aces. Ocular ~concave~ and object ~convex) surfaces ofmultifocal lenses to he produced from the blanks are next
ground to preselected
j b/fin~
- 6a -
~04~3~ .
spherlcal and/or tonlc surface curvatures wtlich are di~posed in
predetermined angular relationships and proxiinitiPs to the blank
lnterfaces according to particular multifocusing properties
desired of lenses to be formed therefrom.
Details oE the invention will become more readily ap-
parent from th~ following description when taken in conjunction
with the accompanying drawings.
IN THE DRAWINGS:
Fig. 1 is a face v`iew of a multifocal lens which is
exemplary of one embodiment of the invention;
Fig. 2 is a cross-sectional view taken generally along
line 2-2 of Fig. 1 with cross-hatching omitted for clarity in
illustrating important details of the lnventlon;
Fig. 3 is a cross-sectlonal vlew of a type of lens
blank from which the lens of Fig. 1, illustrated wlth dot-dash
outline, may be produced; cross-hatching also having been
omitted for ease and clarity of illustration;
Figs. 4, 5, 6; Figs. 7, 8 9; and Figs 10, 11, 12 are
views respectively similar to the views of F:lgs. 1, 2, 3 and
illustrate alternative embodiments of multifocal lenses pro-
ducible according to principles of the invention;
Fig. 13 i5 a cross-sectional view of an apparatus for
making lens blanks according to one aspect of the invention;
Fig. 14 is a cross-sectional view of a mo~ified system
for-producing the lens blanks;
Fig. 15 ls an illustration, in perspective, of an
exemplary lens blank;
Fig. 16 is a perspective view of an alternate form of
lens blank; and
Fig~. 17> 18, 19 and 20 are illustrat~ons, in cross
sectlon, of spparstuses and techniques used to prepsre le~s
` tbl
3~
blanks for the manufacture of various types of multifocal
lenses according to prlnciples of the invention.
DESCRIPTION OF THE PREFERRED E~BODIMENTS
The basic element used for producing multifocal lenses
accor~ing to the present invention is a laminate comprised of a
layer of high refractive index thermoplastic ophthalmic lens
material fused or cemented onto a layer of lower refractive
index lens material.
Referring more particularly to the drawings, blanks 30,
30a, 30b and 30c (Figs. 3, 6, 9 and 12) are exe~plary of lami-
nates which may be used to produce lenses ~2, 32a, 32b, and 32c
(Figs. 1, 4, 7 and 10).
Lenses 32, 32a, 32b and 32c comprise only Q minimum of
many varlations of multifocal lens designs which may be produced
according to this invention. They are exemplary of the more
common types of multifocal lenses, i.e. those most readily and,
accordingly, most facilitative in demonstrating principles of
the invention.
Lens 32 (Fig. 1) is one having a lar~e lower portion R
and a smaller upper portion D.
Fig. 4 illustrates a lens 32a similar to lens 32 but
having a near vision or reading portion R which more conven-
- tionally covers substantially less surface area of the lens
than its distance vision portion D and wherein po~tion R is of
greater refractive power than portion D as is custo~ary in
designing multifocal lenses for hyperopes, for example.
Lens 32b tFigs- 7 and 8) is distinctive in its having a
substantially straight line of division 34 between its reading
portion R and distance portion D wherein these portions extend
co~pletely from edge-to-edge across the lens respectively below
a~d above line 34. Llne 34 i5 produced by a relatively sharp
db/
3[)
~tep Gr ~og along the internal interface of lts component parts
(Fig. 8). This Jog resembles the exposed led~e of a con-
ventional one-piece multifocal lens of the Franklin type.
Accordingly, lens 32b will be referred to hereinafter as a
"Franklin-type" lens but only for ease and clarity of indicating
lts distlnctiveness over other forms of lenses contemplated by
the present invention. No further associat:Lon with conventional
raised ledge lenses is intended by subsequent use of this
expression.
Another type of ~ultifocal lens 32c ~Fig. 10) which may
be produced according to this invention is one having progressive-
ly varying optical powers in directions from its center down-
wardly and outwardly toward its edges. In view of the perform-
ance o~ this lens re~embling that of prior art progressive power
lenses formed by aspherically shaping their outer surfaces, lens
32 will be referred to hereinafter as a "progressive po~er"
multifocal lens.
Referring more particularly to the techniques contemplated
for producing lenses of any one or another of the aforesaid
exemplary types, and variations thereof, Figs. 13-20 illustrate
operations and exemplary equipment useful in forming the basic
lens elements, e.g. laminated lens blanks 30, 30a~ 30b and 30c.
The lens blanks 30, 30a, 30b, 30c which comprise a
layer of high refractive index material fused onto a layer of
; low refractive index material when oxide glasses are used as
the thermoplastic 7ens materials, may be formed individually as
illustrated in Fig. 13. A disc of high refractive index ~lass
36 (e.g. 1.66 index flint) having a highly polished surface 38
is placed upon a similarly highly polished surface 40 of a disc
42 of glass of lower refractive index (e.g. 1.523 index optical
crown). Discs 36 and 42 are assembled internally of an oven or
furnace 44 with a ~pacer 46 of aluminum, steel, platlnum or a
db/
1~)44~3~
wedge of high melting temperature glass posltioned betwe~n ele-
ments 36 and 42 ad~acent one edge thereof. The asse~bly of pieces
36, 42 is gradual~y raised to a fusing temperature (e.g. of from
approxlmately 740C to 760C by conventional heating units 48 con-
trolled in their operation by thermocouples or their equivalent
positioned adjacent the assembly of glasses. During this heating
of the glasses, a gradual settling of disc 36 upon disc 42 in a
diametric direction from one edge tow~rd spacer 46 will force gases
occurring between surfaces 38 and 40 toward spacer 46 and outwardly
of the assembly thereby producing a clean bubble-free fusion inter-
face.
An alternatlve method for preparing similarly fused lens
blanks is illustrated in Fig. 14. This i~cludes furnace 52 having
lehr 54 through which a sheet 56 oE low refractive index op~ical
glass (e.g. crown) i5 moved continuously by conveyor rollers 58.
The sheet 56 of the glass may be formed by any of various con-
ventional sheet glass manufacturing techniques (e.g. the float
glass process~ and directed immediately therefrom into furnace 52.
~he glass ribbon 56 preferably is in the viscous state as drawn
from the tank thus having an upper surface suitable for sub-
sequent fusion to glass 64. If cooled to the rigid state, its
upper surface 60 is polished prior to or upon entering furnace 5~.
Fire polishing ~ith heat from gas burners 62 will produce desirable
results. Various other means such as laser beams may be used to
produce the necessary intense heating effects.
Glass sheet 56 pas~es beneath a supply 64 af molten other
optical glass ~e.g. a high refractive index flint) which is caused
to flow onto surface 60 of sheet 56 and become interfacially fused
thereto. Glass 64 may be applled in granular form, if des$red.
The thus for~ed upper sheet 66 is carried with sheet 56
through furnace 54 wherein the resulting glass laminate is cooled
1~
db/
3~
to a temperature corresponding to a vlscosity of 107 to 104 poises.
After leaving the furnace 54, the laminate 68 is pressed
and cut in presshead 69 to produce lens blanks 70. Blanks 70 may
be circular as shown in Fig. 15 or of various other shapes, e.g.
generally rectangular as illustrated in Fig. 16, whether they are
mass produced as shown in Fig. 14 or individually fo~med BS shown
in Fig. 13. The interface curve shown in Yigs. 17-19 can be pro-
- duced during this pressing operation. The blanks are then trans-
ferred to an annealing lehr by means knowl~ to those skilled in
the art.
To those interested in greater details of glass fusing
furnaces and techniques for producing glass laminates of the afore-
said types may refer to U.S. Patents Nos. 3,148,046 and 3,256,081,
for examp}e.
Menigcus lens blank 30 (Fig. 3) may be formed by slumping
or pressing individually fused blanks 70 as illustrated in Fig. 17.
Slumping ma~ be accomplished by placing one of flat blanks 70
upon support 72 formed of graphite, cast iron or another suitable
glass working tool material. The blank 70 is then heated suf-
ficiently to slump under its own weight (i.e. by the force ofgravity) against curved surface 74 and assume the meniscus shape of
surface 74 as lens blank 30. This shaping operation may be as-
sisted by the use of plunger 76, if desired. Alternatively,
blank 30 may be formed entirely by pressing with plunger 76 and at
a substantially lower operating temperature than that required
for slumping.
~ ens blank 30a (Fig. 6) being substantially identical to
blank 30, may also be formed with the apparatus of Fig. 17
In similar fashion, blank 30b (Fig. 7) may be formed of any
one of flat blanks 70 by slumping andlor pressing in support 78 of
Fig. 18; plunger 80 being used for pressing when desired.
11
db/
3~
Support 82 nnd plunger 84 (Fig. 19) illustrate a modi-
ficatlon of the apparatus of Fig. 18 wherewlth, accordlng to
Fig. 19, a modification of the Franklin-type lcns blank 30b may
be produced. Blank 30b1 (Fig. 19) is provided with an lnter-
mediate section 86 from which an intermedlate vlewing portlon of
a lens ultlmately formed therefrom may be produced. Thus, in ad-
dition to the provision of distance and reading portions, lens
blank 30b1 may be used to produce Franklln-type multifocals having
an intermediate vie~ing portion.
Support 98 and plunger 90 of Fig. 20, having aspherically
curved surfaces 92 and 94 respectively, may be used to slump
and/or press a preselected flat blank 70 into the form of the lens
blank 30c ~Fig. 12).
It is to be understood that supports 78, 82, 88 and
plungers 80, 84, 90 are all constructed of materials normally used
in the glass forming art and which may be selected with ordinary
skili of the artisan. Furthermore, flat blanks 70 may be
slumped or pressed with their high refractive index laminate
facing downwardly as in Fig. 17 or upwardly as shown in Figs. 18-20.
A temperature useful in shaping a flat blank 70 (Fig. lS
or Fig. 16) by slumping agalnst one or another of supports 72, 78,
82 or 88 for example, may range between 740C and 760C for a
laminate of ophthalmic crown glass having an index of refraction of
1.523 and ophthalmic flint glass having an index of refractio~
of 1.66.
A pressing process which would yermit more rapid pro-
duction than can be achieved by slumping and greater capability of
producing more complex shapes such as those of lens blanks 30b
and 30c (Figs. 9 and 12), may be performed with graphite molds
and plungers as follows:
db/
.... . . .
~`~4~3~
With the entire a~sembly of the support, blank70 to be
shaped and plunger placed in a suitable oven and heated to ap-
proximately 710C with a lead of approximately 5 kgs. applied to
the plunger during the entire heating cycle, shaping of the
blank will become completed upon reaching the approximate 710C
temperature. Cooling slowly thereafter over several hours, e.g.
6-10 hours, to appro~imately 100C completes the operation. A
considerable lessening of this pressing time can be achieved by
preheating the flat blank 70 and the particular pressing support
72, 78, 82, 88 and/or plunger 76, 80, 84 used.
The meniscus lens blanks 30, 30a, 30b and 30c, having
interfaces 96 of curved shaped corresponding to their outer sur-
face shapes, are used to produce lenses 32, 32a, 32b and 32c
respectively.
The forming of exemplary finished multifocal ophthalmic
lenses 32, 32a, 32b, and 32c includes a first operation of cut-
ting or grinding away all portions of blanks 30, 30a, 30b, 30c
except those within the dot-dash outlines in Figs. 3, 6, 9 and 12.
These remaining portions of lens blanks 30, 30a, 30b and 30c are,
as illustrated, disposed in particular predetermined angular
relationships and proximities to interfaces 96 each according to
the multifocusing properties desired of the finished lenses 32,
32a, 32b and 32c.
After grinding, these portions of blanks 30, 30a, 30b and
30c which are more clearly illustrated in Figs. 2, 5, 8 and 11
respectively, are polished to the high degree of smoothness
normally afforded ophthalmic lenses.
Those interested in types and details of lens grinding
snd polishing apparatuses useful in performance of the afore-
sald cutting or grindlng a~ay and polishing of lens blanks 30,30a, 30b and 30c to the configurations illustrated by dot-dash
- ~: 1 3
db¦
33~
outline in Figs. 3, 6, 9 and 12 may refer to U.S. Patents Nos.
3,117,396; 3,0g3,939; and 2,994,164, for example.
While these grinding and polishing operations per se are
contemplated as being performed conventionally, a particular
novel and important feature of the grinding and polishing
operations is that of producing lenses 32, 32a, 32b and 32c
from portions of 31, 31a, 31b and 31c of meniscusly shaped lami-
nates (blanks 30, 30a, 30b and 30c) which are disposed in the il-
lustrated particular predetermined angular relationships and
proximities to interface 96. Some of these remaining portions of
blanks 30, 30a, 30b and 30c extend completely across interace 96
(Figs. 3 and 6), another generally parallel to interface 96
~Fig. 9) and still another only partially across interEace 96
(Fig. 12).
Exemplary embodiments of lenses 32, 32a, 32b and 32c
which may be prodaced according to present invention are the
following:
I Lens 32 (Figs. 1 and 2)
1. Index of refraction of glass 66 = 1.523
2. Index of refraction of glass j6 - 1.66
3. Center thickne5s t = 3.4 mm
4. Radius of object side
~convex curvature r ) = 235 mm
5. Radius of ocular si~e
(concave curvature r ) - 167 mm
6. Refractive power of distance
portion D = -2.8 diopters
7. Refractive power of upper part of reading
portion R = -2.1 diopters
8. Refractive power of lower part of reading
portion R = -2.0 diopters
II Lens 32a ~Fi~s. 4 and 5)
1. Index of refraction of glass 66 = 1.523
2. Index of refraction of glass 56 = 1.66
3. Center thickness t = 3.4 mm
4. Radius of ocular side
(concave curvature r2) ~ 167 mm
5. Radius of ob~ect side
(concave curvature rl) ~ 235 mm
6. Refractive power of upper
portlon D = approximately -2.1 diopters
7. Refractive power of lower
portion R ~ approximP~ely -2.8 diopter3
I L~
db t
~4493Q
III Lens 32b ~Fi~s. 7 an~ 8)
1. Index of refraction of glass 56 = 1.53
2. Index of refraction of glass 66 = 1.70
3. Radius of object si~e (convex curvature r1) = 81.5 mm
4. Radius of ocular side (concave curv~ture r2)
= 70.7 mm
5. Refractive power of distance
portion D = approximately -1.65 diopters
6. Refractive power of reading
portion R = approximately -1.00 diopter
(w1th r3 and r4 of respectively different curvature)
IV Lens 32c (Fi~s. 10 and 11)
1. Index of refraction of glass 56 = 1.523
2. Index of refraction of glass 66 = 1.66
3. Radius of object side
(ccnvex curvature r ) = 235 mm
4. Radius of ocular si~e
(concave curvature r2) = 167 mm
It can be seen from the foregoing description that this
invention overcomes problems and difEiculties attending and in-
herent in prlor art multifocal lens manufacturing proces6es by
obviating the hitherto need for grinding and polishing or other-
wise preparing individual lens segments and major portions of
fused style multifocaIs.
The present invention utilizes laminates of high and lo~
refractive index materials provided with interfaces shaped by
slumping or hot pressing according to the multifocusing properties
desired of the finished lenses. The laminates are formed with
dir&ctions of cupping of all curvatures of their outer surfaces
and interfaces being similar, i.e. centers of curvature of outer
surfacea and interfaces being, in each case of each lens blank,
all located at one side only of the blank.
The foregoing laminates are finished with simple and in-
expensive single vision lens processing tools and apparatuses.
For example, complex tools, apparatuses and procedures required
-~` for the production of conventional ~ranklin-type multifocal
lenses and/or conventional progressive power multifocal lenses
are avoided as are the necessities for exceptional skills.
db/
3~
It should also be understood that the above~described
techniques for formlng laminated high and relatlvely low re-
fractive index glasses are ~o be considered as illustrative of
useful practices but not in a limiting sense. The invention con-
templates the use of laminates prepared directly Erom molten
materials such as oxide glasses and which may be immediately
pressed into the desired meniscus and/or other shapes without re-
heating for conservation of both time and fuel energy.
It is further contemplated that the laminates (lens
blanks) may consist of more than two layers of different re-
fractive index materials in instances where greater refractive
index gradientg are required of the finished lenses. For
example, laminates of several layers of lens materials with
step-wise increasing or decreasing refractive index may be used.
Furthermore, such multilayer laminates may be drawn or stretched
to reduce the thickness of their laminae by desired amounts and
their dra~n portions may be cut into segments, reassembled and
redrawn to still further reduce the thickness of individual
laminae and/or double, triple, etc. their number by repeated
reassembllng and redrawing.
db/
