CA1314366C

CA1314366C - Method for designing parametric molding apparatus

Info

Publication number: CA1314366C
Application number: CA000592462A
Authority: CA
Inventors: David P. Spector
Original assignee: Sola Group Ltd
Current assignee: Sola Group Ltd
Priority date: 1988-03-03
Filing date: 1989-03-01
Publication date: 1993-03-16
Anticipated expiration: 2010-03-16
Also published as: US4874561A

Abstract

METHOD FOR DESIGNING PARAMETRIC MOLDING APPARATUS
Abstract of the Invention A method for designing a molding apparatus, especially for molding lenses and the like, comprises defining a nominal mold reference curve disposed between a pair of mold members having smooth, curved surfaces in confronting relationship to define a mold cavity therebetween. A plurality of concave and convex molding members are provided, all having differing molding surface curvatures but identical spacing from the respective curved surface to the nominal reference curve, measured from the point of closest approach of the curved surface to the reference curve. Any paired concave and convex molding surfaces have the same spacing from the reference curve and thus from each other, so that, for example, a universal gasket can be employed to hold any two paired convex and concave molding members in precise spacing, without regard to the curvature of the molding surfaces.
Spector Parametric Molding Application

Description

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Irl the ~ield of manu~acturing ophthalmic lenses, it is generaliy recognized in the pr~or a~ ~at the most economical means of forming ~uch lenses is by molding a lens formin~ material betwee~ dies o~ molding members having smooth optical moldi}lg ~urfaees with t~e approprla~e curvature so impar~ ~he desired optieal propertieæ. Generally ~e len3 formitlg r~aterial is a polymer compouFld, such as an acrylic~ me~acl~la~e, polyc~rbonate, or ~e lik~.
It is evidellt ~at a cr~tical ~actor Ltl ~e moldin~ of lenses is the moldin~
members ~emselves. Ci ~nerally, ~ larg~ plurality oP front surface and rear surPace molds must be pro~ided, each havin~ a unique optical su~ace-forming characteristic. To ~ill a parti~ular ophthalmic prescription, appropriate front ~urface and rear su~ace moIding meInber~ are hosen, an optimal lens th~ckness is ~lculat~d i~or ~e two selected mold~ d a gasket or the lik~ is ei~er ~elected or fabricated to secure ~e mold~ together to ~efine the molding cavity. The cavity is ~en filled wi~ lens eompound, cured or polymerized by heat, radiation, or chemical actio~, and ~e fini~hed le~s is removed from tlle assem~ly~
The process ~u~ above requirs~ a very large numbsr of ~ron~ and rear sur~ace molds~ in or~er to ~111 the hundred~ of thou~ands of oph~aLrnic pr~scriptions commonly required. l~ur~ermo~e, a Iarge number of gasl;ets Spec~r Parametric Molding Applicatio~, P~ge 2 ~

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~ J~ 6 arg req uired ~r ~is process, du~ to ~e fact ~at ~e gaskets must ~rm a seal wlth the variou~ly cunred edge con~lgurations of ~ mold members, and ~at the thic~nes~ of the len~es mu~t be ~etermiIIed by the spacing of mold rnembers created by ~he gaske~s. ~ ~is regard, ~e mold ~pacing i~ g0nerally measur~d between the confrontiIlg optical ~ormi~g surfaces of the mold member~. It is vit~l ~a~ ~he ~nold ~pacing lbe greater than a predetermined mit~imum, bo~ to produce a lens of suf~lcient ~hic~nes~ and s~reng~, and to prevent mold çrash~ng and m~tual de~truc~
The large number of mold members and gaskets that must be inve~toried to carry out the proc~s~ de~cribed above represent~ a con~iderable capital investment which is difficult to recollp through commercial sales. l~ere~ore it has been necess~ry in the prior art to s~mplify the process by reducing ~e number of co~poI~ents inventoried. The most s~raightforward simpli~icatioIl is t~ mold len6es h~v~g the desired front ~ur~ace ~nd a stock rear ~urgace (or vic~-ver~a~ ~a~ Gan be ground to ~e desired ~ ished lens by a dispensing optical la~oratory or the li~e. ~i~
tactic introduces a post-rnaflui~acturin l~bor expense, and requires traiIled personnel for high quali~y ~ SO Pur~em~ore, i~ ot an improvement in the p~ior ar~ moldin~ ~echnology, but r~ r an expedient shortcut to mal~:e the tech~ology ~ommercially viable. There is ~ obvious need ~tl the prior art for a molding me~hodology that reduc~ the number of molding Spector Parametric Molding Applicationp Page 3 component~ whil~ provid~ng th~ capability of filling th~ large number of cornmorl ophfflalmic prc~oriptioru.

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Spector Parametric Moldillg ApplicatIon, Pa~e 4 ~J ~

1 3 1 4;5~6 The lpre~ent inventio~ generally compris~s a me~od for d~signing molding c~mpone~ts, and particula~ly lens molding compo~ents. ~ æalient feature of the invetltioll i3 th~ it red~ces ~e ~umber of moldiIlg die~, compared to prior art molding tec~ology, requir~d to produce the same variety of oph~ic len~es. l?~l~ermore, in molding proeess~s requiring gaske~ or the like to secu~ two molding mem~ers togethe~ to ~orm a molding cavity~ ~e number and Yariety of gaskets required i~ r~duced to a ~ery great exten~.
The me~od ~or designi~lg a molding apparatus, especially fQr rnolding lenaes and the like, comprises defining a nominal mold reference eurve disposed between a pair of mold members h~ving smoo~, eurved surfaces in confronting relationship to de~ne a mold cavity ~erebetwe~n, It is p~ssible to d~fine a smgle value of re~e~nce curvature such ~ha~ all lenses within a typical design family are ~oisect~d by thi~ ima~ginary ~u~face without erf~rence; ~at is so that for all plu~ lenses, ~ roI}t curre 2 reference curve ~ back ~rve, and ~or all minus l~nses, back ~urve ~ erellce cu~e 2: front cur~e.
This phenomenon i~ a result of ~e optical and physical u~liformi~ of hurnan eye and fiacial ~eatures, aIld ha~ been discussed in ~ prior art.

Spector Parametric Molding ~pplicatioll, Pa e ~

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A plurality of concave and convex molding members are provided, all having di~fering molding wrface curvatures bu~ ide~t~al 3pacing from the respe~tive curved ~ur~ace to. ~e ~ominal ~ferenco cllrve, measured from ~e poin~ of closest approacll of ~e curved surace to ~e re~erence e~r~fe. (That is~ between ~e center of a negati~e len~ and t~e r~feren~e cu~e, or between ~e edge ~ a po3itive lens and ~e r~fe~nce curve.) Any palred concave and convex molding s~r~ces haYe the same spacing from the r~rence cu~ve a~d thus ~om ea~ ot~ier, so that, for exa~nple, a universal gasket can be employed to hold ar~y two 1?aired convex and collcave mold~n~ n~embers i~ precis~ spacing, withol t regard to the curvature of ~e molding su~aees. Thus ~ly lens formed by ~e method of the present mvention comprisei~ two indivisable portions: a front portior extending from the :reference curve ~o the froIlt su~ace, and a re~r portios extending from tlle reference su~ace ~ the rear surface.

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13~366 ~ igure 1 is a cro~s-~eetiQnal elevation of a lf~ns molding assembly arranged accord~ng to the pre~ent invention and employing a ~gask~t sleeve to join th~ mvldir~ m~mbe~ in a cas~ g a~sembly.

~ igure 2 i~ a cros~-section~sl eIevation of a len~ mQlding a~embly arranged according to the present inverltion and employing çompre~sion moldin~ compone~ to fonn a lens.

~pector Parametric Molding Application~ P~ge 7 13 1 4~h l~L~

The presen~ inv~ntioll generally co~npri3es a met~od for desig~ing mvlding components, and particularly lens moldin~ components. The me~hod is directed ~oward a lerl~ molding ~y~tem that is capable of filling a large portion of the most common oph~almic p~scriptions, using a plurality of molding die~ :fiar le6s numerou~ ~an ~y prio~ art lems mold~ng technique.
Wi~ regard to Figure 1, ~e pre~ent ir~v~ntion pxovides a plurality of ~ont ~urface moldiIlg dies, ~epresen~ed ~ the moldin~ die 11 having a concave optical molding surPace 1~, and a plurality of ~ear su~face moldin~
dies, represented by t~e molding die 13 havi~g a convex opt~cal molding sufface 14. The mol~ing surface~ 12 and 14 may ~ fosrn~d by grinding and polishin~ a glass or me~al material, or by electrodeposi~ivn on. previously fo~med optical surfaces, bo~ :tec~iqucs being well known in ~e pr~or art.
In the embodime~t of Pi$ure 1, both ~ are generally cylLndrical, with tho ax~s o~ ~be cylinder~ generalIy passing through the central po~tions of the respective molding ~urfaces. The die 11 i8 p~ovided with a flange 16 extending radially outwardly from ~he die alrld spaced axially fro~ the surface 12, and the dle 13 iB provided wi~ a flange 17, also extending radia~ly outwardly from ~ di~ d ~paced a~cially from ~e su~ace 14. The flange~ 16 and 17 ars provided wi~ annular ~ur~ace~ 18 and 19, respectively, tha~ are dispoxed ~ confrontin~g, spaced apart relationship.

Spector Parametric MoldLng ~pplicatioll, Page 8 1 3 1 ~;~66 rhe inYen~ion also includes ~ gaske~ or ~leeYe 21 adapted ~o,ioin together the ~wo ~ies in a casting a~sembly. Ihe sleeve is generally ~ylindrical in configura~ion, wi~ a diameter su~ficient to ~m~ a sealing engagement about ~e periphera:l surface~ o:f bo~ dies, with ~e ends o~ ~e sleeve 21 in abut~ing relationship wit~ ~he ~anges lS and 17. The leIlgth of she sleeve between ~e two flan~es 16 and 17 i~ gene~rally constant and the same for any com~ination ~ dies 11 and 13.
An lmportant feature of ~ pr~sent invention is ~e esta~ishment of a reference curve 22 disposed between ~e molding surfaces 1~ and 14. The referencc cur~e represents ~e nominal plano curve of ~e leIlses produced by this method; i.e., a plano lens has both front a~l rear surfaces extending parallel to the ~eference curYe. The reference curve 22 is also used to establls}~ the prope~ spacing of the die~ arld of ~e molding ~urf~ces 12 and 14. Throu~hout the plura}ity of dies 11 and 13, ~e spaeing of ~e surface 12 and the refer~nce curve 2'~- is ~xed ~d iden~icalj ancl the spaeing of the surfaee 14 and the refer~nce cu~ve ~ iB ~ikewise fixed and identical. The spacing betwee~ the ~urfaee~ 1~ or 14 and ~e ~eference curve is measured fr~m th~ point of closest approach of t~e moldi~ surfac~ to ~e leference curve. 'rhis factor dete~nines ~at ei~er the ccnter of a negative.len~, or ~e edge of a positive lens molded accordin~g to ~e presen~ invention will have a fixed ~hickness9 th~oughou~ ~e r~n~e of oph~almic p~',9~ptiOIlS.

Spe~tor Parametric ~olding Applicatioll~ Pag,e 9 ~rr . I r~t l r , . ~ S. ~ 31~

1 3 1 ~366 It is significallt to i~ote ~at ~e ~e 16 i~ disposed ~t a predeteranined axial diseance from ~he su~face 12, and ~ flange 17 i3 likewise disp~sed at a predete~mined axial di~ance from ~e ~urface 14. Thus the dislance X
between the ~ ge surface 18 and th~ reference curve, and ~he distancs Y
from the flange ~u~face 19 and ~e re~e~ence curve is fixed in the. cas~in~
assembly by the sleeve, regardles~ OI ~h8 dies selected to form a particular lens.
~ o employ ~e inven~ioIl as described in Figure 1, ~ies 11 and 13 ar~
select~d in accordance wi~ the oph~almic p~escription to be Pilled, and a sleeve 21 i5 selected wi~ a length that assu~s that ~e optlcal forming surfaces 12 and 14 are spaced apart from the re~ereIlce curve by the predetermined, fixed dis~ancc. L~ns casting compound is then in~roduced into tbe cavity def~ned bet~veen the mold~ng surfaces and ~e sleeve interior surface, by injection or the like, and the compound is cured or polymerized to form ~e ~inished lens. ~he sleeve iB thell removed, ~nd ~he ~ tripped from ~e die~. The die~ may ~en be cleaned and stored for reuse.
A further embodinnent of ~e p~esent invention, depicted in ~igur 2, is adapt~d to fonrl lense~ by compression molding, usLn~ ~e principles elucidated in ~e embodiment of Pi~gu~ 1. A pair of mo~ding dies 11' and 13' a~e provided with op~ical formi~ surface~ 12' and 14', as dsscri~ed preYiously. In ~ embodiment, the dies are provided with ~mooth peripheral wa~ls, and a re dimen~ioned to be slidably received wi~hin the bore Spector Parametric Molding ~pplication, Pa~e 10 131~366 32 of a cylindriGal ~lee~re 31. A~ before, t~e moldi~g sur~aces 12' ~d 14' are positioned at a fixed, constant di~tanc~ from a refersnce curve 21'. The ~ie 11' is seeured ~o a piseon 33 aligned coa~ially with ~ sleeY~ 3~ , alld ~e die 13' i~ s0cured to a coaxial pistorl 3~. A pair of piston stops 3S and 37 are also provided to limit the travel oiF the respective pistons 33 and 34 toward the referenee cllrve 21' ~o ~istfl~ces X' and Y'. The d;stances X' and 'Y' are calcula~ed so tha~ the ~lding ~urfaces 12' and 14' can be moved cur~ve by ~eir respective pist~ns toward the reference curve only a~ close as e~e spacing limit ~rom the ref~ren~e curv~.
In the ~mbodime~t of ~igure 2, a pair o~ dies ll' and 13' are selected ~ accordAnc~ with ~e ophthalmic pre~cr~ptioIl ~o be filled, and ~Ihe dies are a~sembled to ~ir respective pi~tons. A ~harge of len~-fo~nimg material is ~t~oduced into the ~re 32 between ~e dies, ~nd ~e die~ are moYed ~o~ether by the piston~ to comp~ss ~ lellD ~o~ning material and mold it into ~e shape dete~ ed by the ~ur~acs~ }2' and 14'. Tlu~ material is th~n solidified by curing, polymeFiz~tioIl, cooling, or the like, depending on the composition and propertie~ of ~e mate~al. l['he pistons are ~en retracted, ~d the fini~hed i~:n3 is ~tripped from ~e die~. The dies may then be removed, cleaned, and stored for future use.
In the method d~picted in Pigure 2, dhe lens fonning materi~l may be ~iected into ~e cavity wi~in ~e cyli~der, wi~ ~e dies inserted t~ ~e limit , Spector parAmetr~c Molding ~plication, Pa~e 11 `

131~366 determinecl by the stops 36 and 37, as i~l prior art injection molding tecblliques. L,i1cewise, a hybrid len~ fo~mmg techniqlle employing inj~ction of th~ material ~ollowed by compressi~n of the dies mày also be practiced wi~in ~he gcope of ~ ~ve~tion.
:: The method described wi~h regard to l~igures 1 and 2, te~ed ~he parametric mold d~sign, llot only p~oducos lenses of ux~ or~ ~ickness, it also minimize~ the number of dies requ;red to produce a ~ull range of multifocal le~lse3~ either ~tock le~ses (wi~oue cylinder power) or finished lenses wi~ cylin~er power. For exampl0, th~ ~ollowing tabl~ illustrates a comparison oP th0 parametric d~sign me~od wi~ a ~ypical prior ar~ lens molding ~ystem for pro~ucing 75 mm ClR39 stoc~ le~ses in a range o~ ~:fa~e power~ from ~4.00D to ~-4.l:)0D. Add powe~ a~ 0.25 diopter incremeIlts to ~3.00D, and cy~n~er power~ are in 0.25 diopt~r inerements to -2.00D;

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Par~metnc Pronts S ~S 6~
Parame~ric back~ 153 17 153 TOTAL 158 82 2l8 Spec~or Parametric Molding ~pplication, Page 12 1 31 -~366 CR39 i~ronts 33 429 429 CR~9 ba~s 63 7 63 ~ e parametric mold desigll method ~us requires ~58 mold dies ~o produce the ~ull r~nge of len6e~, wh;le ~ prlor art ~meth~d requlre~ 1024 die~. Thus it is apparent ~at ~e pr~seIlt in~eIlt~orl obtain~ ~u~stantial sav~gs, not only in the high capit~l ~o~ts as~ociated wi~ procuring rnolding die6, but also in maintaining a large iDLve~ory o~ die~. Pur~ermor~, the present ~nvention prevents clQshin~ of ~e dies in ~e molding process, ~n event ~at occur~ occassionally in prior art mold~ng ~ys~ems alld results in destmctio~
of the dies.

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Spector Parametric h~olding Application, Pa~e 13

Claims

1. A method for producing ophthalmic lenses, comprising the steps of providing a first plurality of front surface molding dies having concave optical forming surfaces, providing a second plurality of rear surface molding dies having convex optical joining surfaces, selecting a front surface molding die and a rear surface molding die from said pluralities of dies, defining an imaginary molding reference curve, joining said selected molding dies in confronting relationship in a molding assembly with said concave. optical forming surface disposed at a first fixed distance from said molding reference curve and said convex optical forming surface disposed at a second fixed distance from said molding reference curve, and thereafter molding a lens between said dies.

2. The method of claim 1, wherein said first fixed distance from said reference curve and said second fixed distance from said reference curve are both constants for any of said first and second plurality of dies.

3. The method of claim 2, wherein said reference curve is disposed between said confronting dies.

Spector Parametric Molding Application, Page 14

4. The method of claim 3, further including providing a sleeve for joining said selected dies together in a lens casting assembly, said sleeve maintaining said first and second fixed distances of said dies from said reference curve.

5. The method of claim 3, further including providing a bore for receiving said selected dies in slidably translating fashion therein in a compression molding assembly.

Spector Parametric Molding Application, Page 15