US2595360A - Equatorial generator for multiple lens grinding - Google Patents

Description

y 1952 A. J. HOLMAN 2,595,360

EQUATORIAL GENERATOR FOR MULTIPLE LENS GRINDING Filed Feb. 7, 1947 4 Sheets-Sheet l y 6, 1952 A. J. HOLMAN 2,595,360

EQUATORIAL GENERATOR FOR MULTIPLE LENS GRINDING Filed Feb. '7, 1947 4 Sheets-Sheet 2 x 2 I m E W 5 I 2 Q I a E 3 Q 1 3 I Q N I E I R- 2 5 Ro E w 2 l 1% y 6, 1952 A. J. HOLMAN 2,595,360

EQUATORIAL GENERATOR FOR MULTIPLE LENS GRINDING Filed Feb. 7, 1947 4 Sheets-Sheet 5 M y 6, 1952 A. J. HOLMAN 2,595,360

EQUATORIAL GENERATOR FOR MULTIPLE LENS GRINDING Filed Feb. 7, 1947 4 Sheets-Sheet 4 lllllllllll ll[IIIIIIIIIIIIIl!lll| lllllllllllllllllllllll W N W My. //4w/.

Patented May 6, 1952 EQUATORIAL GENERATOR FOR MULTIPLE LENS GRINDING Ar u -L Holm n, Br g t n, Nils App i a n F uar 194.7, erialNo-IZZZM.

1 My invention relates to apparatus and methods for grinding curved surface on glass or other transparent materials and more especially to precision generator grinding of lens blanks in multiple by diamond milling over equatorial zones of a spherical carrier. The present device is an improvement over the mechanism described in copending-patent application Serial No. 583,244, filed March 1-7, 1945, and which issued as Patent No. 2,510,133 on June 6, 1950, entitled Method and Machine for Grinding Lenses, of which I am co-in-ventor; The former apparatus does good grinding and serves well the purpose for which it was designed, namely, continuous production of finish ground surfaces on lens blanks which are attached, one by one, to the circular chuck holder before grinding and are removed therefrom, one ata time, after grinding while the chuck holder is being rotated continuously at suitable lens blank feeding rate. For polishing, these lens blanks must be remounted and, if they are polished singly, a varylarge number of spindles are required for volume production: if the ground blanks are mounted in multiple on chucks, great skill and accuracy are required to so mount them that the surface of each lens blank lies on a common spherical surface, otherwise there will be high. lowand tipped surfaces and polishing time will be excessively long,- particularly if the block is to be generator polished. If the block is polished on an ordinary spindle polisher, polishingtime is still long and rejections rise seriously with inaccurate mounting of ground blanks.

The principal object of the present invention is to provide an equipment and a method of procedure to eliminate the necessity for remounting finish ground lens blanks forpolishing. When this is accomplished successfully, the fine ground blanks can be polished very quickly and with great accuracy in-a suitable polishing machine employing the generating principle, a machine wherein the relative movements of the lens blanks and the polishing elements produce true curvature on the work and maintain correct curvature of the polishing elements. The complete accomplishment ofthis principal object involves considerable invention including an improved lens blank carrier, an'improved diamond milling generator adapted and arranged to handle the new lens blank carrier and a new generator polishing ma- 10 Claims. (Cl. 51-.73)

the methods bywhich they function. The new generator polishing machine is the subject of my copendingpatent application Serial No. 739,011

filed April 2, 1947, and which issued as Patent No! Serial No. 583,244 hereinbefore referred to, also my copending patent application Serial No.

589,983, filed April 24, 1945, and which issued" as Patent No. 2,541,823 on February 13, 195-1, for Lens Grinding Tool and Method, that, asabrading material is-worn away, bycontinued grinding of lens blanks, the boreof the grinding rings will become enlarged. Asa result, each successive lens blank is ground to a very slightly: longer radiusof curvature. With suitable diamond milling rings, it is expected that several hundred lens blanks can be ground for each one thousandth inch of; wear on the grindingrings, nevertheless, when each diamond milling generator grinds several thousand lens blanks a day, the total wear-on the grinding rings in a months service will represent perhaps one'sixteenth of a diopterdiiference in refracting power of the curved surface of the lens. Improved mounting of the grinding rings and a better ring structure permit adjustment of the bore of the grinding rings to limit, to any prescribed tolerance, the variation in curvature of 1 surface ground on lens; blanks.

Another object of this invention is to so form the grinding rings as to eliminate the necessity chine which will polish quickly all the fine ground lens blanks on the carriers as they come from the diamond milling generator. The present application covers the improved diamond milling generator and the improved lens blank carrier, also for spacer rings between the grinding-ringsprogressively graded as to grit size and cutting speed; thereby simplifying the structures, eliminating loose parts, improving the distribution of coolant to the grinding areas, providing more effective scavenging of ground materials and eliminating completely all shoulder" grinding; i. e., grinding of lens blanks against the edge of a grinding ring as distinguished from grinding of the blanks by the abrading material covering the cylindrical bore of the grinding rings. Elimination of shoulder grinding is important for several reasons: shoulder grinding invariably deforms the grinding tool, splinters-the blanks, makes scavenging of'groun'd material more difficult and decreasessubstantially the rate at which lens blanks may be fed to the grinding rings.

Another objectof this invention relating'to the generating of; spherical surfaces, is to arrange the progressively graded grinding rings in such manner that lens blanks may be presented to the grinding rings from two directions for combined rough and fine grinding thereby permitting, (1) rotation of the carrier when fully loaded with lens blanks to be ground and, (2) complete grinding of all lens blanks on the carrier when the carrier has been rotated through an angle of 180 degrees.

A further object of this invention is to arrange the lens blanks on the surface of the carrier in such manner that the carrier may be brought to its proper grinding position, within the grinding rings, without grinding any lens blank down, at any point, to the depth of the ultimate finish ground surface.

Further objects are to increase the rigidity of the structures supporting the lens blank carrier so the carrier may be always precisely positioned within the grinding rings and may be so substantially supported as to permit rapid feeding of lens blanks to the grinding rings without causing chattering at the grinding surfaces; providing simple means for mounting the carrier in the supporting structures, feeding the carrier into grinding position, rotating the carrier to feed lens blanks to the grinding rings, withdrawing the carrier from grinding position and removing the carrier from its supporting structures.

Another object is to provide simple and eifective means whereby toric surfaces may be generated in multiple on a suitable lens blank carrier and may be polished subsequently in multiple.

Still another object of the invention is to provide simple mean whereby the carrier supporting and feeding structures may be easily and quickly swung out of operating position to permit free access to the grinding rings for dressing, for adjustment to compensate for wear, or for replacement.

The ultimate object of this invention is development of the method for rapid production of lens blanks finish ground in multiple to a common spherical surface to specified curvature, said lens blanks being supported on a carrier suitable for L insertion, subsequent to grinding, into a generator polishing machine wherein the fine ground spherical surface common to all lens blanks on the carrier may be polished quickly and accurately without departure from true spherical form.

This diamond milling generator is fully enclosed so that coolant most satisfactory for rapid cutting may be used without messing up either the operating personnel or the premises wherein the equipment is used. Coolant is fed to the grinding rings under pressure and is withdrawn from the generator, preferably, under partial vacuum to insure minimum leakage of coolant charged with ground material and maximum recovery of diamond grit loosened by grinding action. The machine is designed for large volume production and may be used for making precision optics but it will probably find its greatest use in the manufacture of ophthalmic lenses which are produced annually by the millions in this country. The device is not limited in design to any particular spherical or toric curvature, as suitable structures may be built to generate any curvature of lens surface from ten diopter to two diopter, or even beyond these limits, and each particular size carrier will accommodate from 100 to 150 per cent more lens blanks than can be ground successfully on chucks in conventional lens lapping machines or in diamond milling machines employing cup type wheels. Moreover,

since this device is a generating grinder, the yield of first quality product is better than per cent whereas the current yield of first quality product with lens lapping machines is often as low as 40 per cent and seldom exceeds 55 per cent in plants where inspection is critical and a high standard is maintained. Each lens made in this device is ground with its optical center at the geometrical center of the blank, hence therewill be no discarding of lenses which will not center out in edging. Because of this fact, blanks should be edged to finish size before being mounted on the lens blank carrier, thereby saving unnecessary grinding and polishing of lens surface which is eventually ground away in theedging process. It is expected that this diamond milling generator will effect a reduction of at least 50 per cent in cost of grinding ophthalmic lens blanks. Since the product of this generator is finish ground lens blanks so supported in multiple on a carrier that their ground faces lie on a common spherical surface, the carrier may be transferred to a generator polishing machine wherein polishing of all blanks on the carrier may be effected, in one operation, quickly and without distortion. Thus, this method of grinding is effective, not only in reducing grinding costs, but also in reducing the cost of subsequent polishing of the lenses.

It seems in order to point out the primary characteristic of this invention which distinguishes it from other diamond milling generators. During the recent war, many diamond milling generators were built which employed a cup type diamond milling tool. In these devices, any cup tool will grind any and all curvatures, within reason, on lens blanks depending on the angle formed between the axis of rotation of the tool and the axis of rotation of the lens blank in any particular set up of the the generator. Essentially, these devices grind only the polar cap of a sphere: this polar cap may consist of one single lens blank or it may include multiple lens blanks carried on a shell but in no event is it possible to grind successfully surfaces approaching a hemisphere in extent, 1. e., surfaces comprising degrees solid angle. In many respects, this polar cap grinding is similar to the grinding done in ordinary lens lapping machines which operate today, basically, after the fashion used for centuries in grinding lens surfaces. The distinguishing characteristic of my new diamond milling generator is the fact that it grinds surfaces on a sphere adjacent to the equator and does not grind at all on the polar caps because these areas are utilized for mechanical support of the polar axis whereon the sphere is rotated. Specifically, then, my improved diamond milling generator is an equatorial grinder whereas all other diamond milling generators, as well as all lens lapping machines, are polar cap grinders.

My device and the method of its operation may be best understood by reference to the drawings in which: a

Fig. 1 is a plan view, at quarter scale, of the complete machine,

Fig. 2 is a front elevation, at quarter scale, of the complete machine,

Fig. 3 is an end elevation, at quarter scale, of the complete machine,

Fig. 4 is a partial vertical cross section, at half scale, in the plane of the axis of rotation of the tool,

Fig. 5 is an elevation, at half scale, of the lens blank carrier,

Fig.1 'i is at cross section", at iull "scale; through the grinding rings+and the= adjacentportion of v the tool supporting shell,

1 Fig. 8 isacross' section; at full-scale; on line B -8 0i lili'g. 7 showing coolant circulation channet's;

Fig; 9 is'across section, at -full scale;similar to Fig; 7 but= showing a; di iferent arrangement of grinding rings,

Fig.- I0' is -a=-view,' atfuI-l scale, of the portion of the-abrading face of a rough grindingring showingshape of coolant circulationchannels,

Fig; 11=is'-a=-view; at half scale,- ofafine grind ing showing key structure removable to permit periodic adjustment of the'bore-ofthe r Fig. 12 is a diagrammatic equatorial section, at full scale; illustrating positioning of lens blanks onthe spherical carrier,

Fig. 13 is a diagrammaticmeridian section, at full scale, illustrating positioning of lens blanks on the sphericalcarrier.

Fig. 14' is a diagrammatic'view, at half scale, of a special six curve lens blank carrier positioned' within a five curve" grinding rin for, generating toric surface;

Fig; 15 is a sectional view, at half'scale, on

line'I5''I5- of Fig; 14 showin -positioning of axis of'carrier with respectto grinding ringsfor'gene eratingtoricsurface.

Referring now' more specifically to theidi awings in which like reference numerals. indicate like parts, albase' I. (Figs.1,.2', 3 and.4) of heavy cast metal is provided with two setsofintegral machined bosses whereonare securely held and accurately alignedb'earing brackets 2i and 3 each of which. houses a. precision cylindrical roller bearing. as indicated at 4 (Fig. 4). A rotating tool. unit, comprising hollow shaft. 5 and tool supporting shell. 6 suitably. press fitted .or shrunk together as shown .withinbearing 4', is journaled in bearing brackets 2. and. 3, and. a. pulley 1 arranged formultiple. V belt drive is suitably secured to shaft 5. T'oolsupporting shell 6 has an accurately machined cylindrical bore at its end of larger diameter wherein-are snugly fitted, .to prevent-turning within the bore,,multiple-grinding rings comprising, from left to right (Figs. 4

and 7), rough grinding. ring 8, fine grinding ring 9, and a second rough grinding ring In which is exactly like rough grinding ring 8 in composition andv structure. A flanged retaining ring I I, secured to the end of tool supporting shell 6 by suitable screws, serves to retain the grinding rings'in proper operating position in the tool supporting shell. Grinding rings 8, 9 and I0, collectively, comprise the diamond milling tool. The tool supportin shell is enclosed in a split housing, lower portion I2. (Figs. 2 and 4) being secured by suitable bolts to machined pads on base I and upper portion I3 being secured to lower portion I2 by suitable bolts, all as shown in Fig. 2. A flanged ring I4, containing an accurate bore centered onthe axis of rotation of tool supporting shell 6 and havingan outer face square to said axis, is secured by suitable'screws and a flanged fit to upper and lower portions I3. and I2 of the split housing.

Free circulation of coolant to the. tool is sup.- plied in the following manner: A bore I5 (Fig.4)

which .runs: thezlength .o fjhollowwshaitii', -,carriesr coolant, supplied: from a: suitable. source, through a connection .(not showmuwiththeoutboardjend ofishaftri, to the circular: chamber-z I6 in the hub: of tool supporting shell 6, circular chamber" I5 being-formed partly by the inner-end of shaft '5, partly by a. plug. I'I closing therbore; in; thehub. of tool: supporting shellB; andpartlyby an annular recess; turned. in the hub; of toolsupporting shell 6. From circular-chamber I 6, coolant flows through a plurality of holes drilled in. the: body; of tool supporting shell 6 all the way to the inner face of. flanged. retaining ring. II which covers the ends of these'. drilled holes: In four; axial positions. under the grinding'rings', saw cuts..I.8. (Figs. 4, 7 and 8) are made'in .the tool seating bore ofll tool supportingxshell. 6; into; each drilled hole to a depth of. half the diameter of the drilled hole. Rough grindin rings 8- and. I0, composed of sintered powdered metal, are. formed on their annular-faces; as shown in Fig; 8, with curved recesses I9 extending. each way from each drilled hole in tool supporting'shell 6, and with radial semicircular depressions 20 (Fig. 10') which con-- nect curved recesses I9 with the abrading surfaces of the rough grinding rings. Thus, after the multiple grinding rings have been inserted in the tool supporting shell 6, there are many *passages for circulation of coolant distributeduniformly across the face and around the circumference of the abradin surface of the-diamond milling tool. Coolant flowing to the right from the grinding tool (Fig. 4) will find its way over tool retaining ring II into the tool housing; coolant flowing to the left will pass into the housing; throughholes through tool supporting; shell. 6 asshown in ;the cross section-at top of. Fig. 4. All coolant will bewithdrawn-underrp'aF tial' vacuum from the-tool. housing through the opening in the -bottom thereof.

In cases where an unusually large amount of glass is to be removed from the surface of lens blanks or where fused bifocal flint blanks areto bezground as shown diagrammatically in Fig. 12; it is preferable to arrange the grinding rings as shown in Fig. 9, wherein fine grinding ringa has on either side. a rough grinding ring ZI provided on each annular face with coolantcirculation' depressions. as in Fig. 8, and each rough grinding ring 21 is, in turn, flanked with a rough grinding ring 22 provided with a beveled edge which is first to contactlens blanks as they are fed to the grinding tool. This arrangeent of tool elements in the tool supporting shellv can accommodate a grinding cut to a depth indicated as b (Fig. .'9)' without direct shoulder grinding whereas the tool arrangement shown in Fig. 7 can accommodatea grinding out only to depth. 0 before. shoulder grinding begins. While on the subject of shoulder. grinding, it is wellto point out the. advantage gained. by molding coolant circulation channels in the roughv grinding rings versus employing spacer rings to provide coolant circulationchannels. It will be evident from examination of Figs. 8 and 10 that rough grinding rings are in contact withannular faces of thefine grinding ring at all areas around the circumference of the tool, except. at areas. opposite semicircular depressions 20, hence there is no cylindrical zonejon the face: of: the; abrading tool where no. grinding takes place; If spacer rings are employed between the grinding rings, then there will be a non-grinding cylindrical zone at the tool surface opposite each spacer ring and this will mean shoulder grinding against the annular. faces of line grindin'g'ring 9. This condition would cause rapid wearing of the fine grinding ring, due to overloading, and would limit seriously the rate at which lens blanks can be fed to the grinding tool.

From calculations based on data showing rate of wear of cup type diamond wheels, it is estimated conservatively that, in an equatorial diamond milling generator designed to generate "six curve surface (i. e., cylindrical bore of grinding tool is ,4; meter), which is the machine illustrated in the drawings, about 600 lens blanks of 52 mm. diameter will be ground for each one thousandth inch radial wear on the grinding tool. Standard tolerance in ophthalmic lens production seems to be '1 s diopter. Such tolerance on a "six curve generator means that the bore or the grinding tool may increase, due to wear in grinding, by .0677 inch in diameter before it need be readjusted, hence it is estimated that about 40,000 lens blanks may be ground before normaltool wear will exceed standard tolerances in lensjsurface refracting power. It is further estimated that the present equatorial grinding generator will grind about 200 lens blanks per hour, hence the bore of the grinding tool will not require adjusting to compensate for normal wear till the generator has operated 40,000/200 or approximately 200 hours or 25 eight hour shifts which is about once each month if the generator is operated eight hours a day.

- In manufacturing diamond abrading wheels in which the sintered abrading material is bonded to steel or other solid metal supporting structure, it has been found difficult and uneconomical to make the diamond impregnated layer much less than ginch in depth In my improved grinding rings I propose to use sintered powdered metal throughout the entire ring, the diamond grit impregnation going to a depth of inch or less as shown by the broken line drawn across the grinding ring sections in Figs. 7 and 9, and by the circle drawn on the annular face of fine grinding ring 9 shown in Fig. 11. I also propose to make the grinding rings with a removable radial key section as shown in Fig. 8 at 60 and in Fig. 11 at 61. When wear on the grinding rings approaches the limit prescribedby tolerance. invariation of lens surface curvature, the grinding rings are removed from the tool supporting shell 6, the radial key section is removed from each grinding ring and is replaced by a narrower radial key section the width of which, circumferentially, is just sufiicient to restore the grinding ring to its original bore when the ring is sprung so both its ends make contact with the new and narrower radial key section. This operation will, of course, reduce the outside diameter of the grinding ring and suitable shim rings will be required around the grinding rings when they are reinserted in the cylindrical bore in tool supporting shell 6. A shim ring common to all grinding rings in the tool may be used if it is suitably perforated to permit free flow of coolant through the tool. Combined shim rings and radial key section sets may be made up in advance and stocked for use when required. Sin- (tered powdered metal grinding rings are easily molded to provide coolant circulation channels as specified, the problem of bonding the diamond grit impregnated sintered powdered metal on steel or other metallic supporting rings is eliminated, and sintered powdered metal rings may be sprung easily in the manner hereinbefore described and without damage to the diamond impregnated layer. Thus, my improved grinding ring structures are particularly advantageous'ior use in my equatorial diamond milling generator.

A spherical lens blank carrier 23 (Figs. 4, 5 and 6), with polar caps removed, is provided with a plurality of recesses wherein lens blanks fit with slight clearance, each recess having a ring seat 24 of smaller diameter than the recess whereon the lens blank rests independently of its peripheral edge as shown in Fig. 13, each ring seat being square to and centered on a radius of the spherical surface of the carrier and positioned at the same radial distance from the center thereof. It is obviously advantageous to support molded lens blanks independently of their peripheral edges because, when lens blanks are so mounted, irregularities in molded peripheral edges cannot cause tilting of lens blanks on their seats. Fig. 5 showsthe arrangement of lens blanks on the carrier asviewed in elevation. Fig. 6 shows the arrangement of lens blanks on the carrier as viewed in plan. Fig. 4 shows the internal structure of the carrier which comprises a lower-section 25 and an upper section 26 between which sections is seated equatorial ring gear 21, the latter being prevented from rotating with respect to sections 25 and 26 by dowel pin 28 which passes through gear 21 and enters both sections of the carrier. A conical journal stud 29 provided with an integral notched ring suitable to be engaged by a socket wrench, is seated on the bottom of a recess in upper section 26 and fits snugly in an axial bore through upper section 26 and lower section 25, the lower end of conical journal stud 29, of somewhat smaller diameter, being threaded to fit accurately in the threaded bore of conical journal sleeve .30. The body of conical journal sleeve 30,is the same diameter as conical journal stud 29, and fits snugly [in the axial bore through lower section 25 of the carrier; the head of conical journal sleeve 30 is the exact counterpart of the head of conical journal stud 29 and is seated on the bottom of a recess in the bottom of lower section 25. By using a pair of socket wrenches, conical journal sleeve 30 is screwed tightly on conical journal stud 29 thereby locking all parts of lens blank carrier 23 together and also providing a pair of accurately aligned and correctly spaced axial conical journals. Conical journal stud 29 and conical journal sleeve 30 are, preferably, hardened and ground all over. The body of lens blank carrier 23 may be made of Dow metal for lightness and strength and, in the larger sizes, the carrier may be made hollow.

It will be observed from examination of Figs. 5 and 6 that the lens blanks are not equally spaced around the carrier 23, but at one great polar circle the spacing between lens blanks is greater than at any other place on the surface of'the carrier. Examination of diagrammatic'Fig. 12 shows the reason for this planned irregularity in spacing of lens blanks. In Fig. 12 the rectangle represents the outlines of the cross section of the grinding tool with the line representing the grinding surface extended beyond each edge of the grinding tool. Ihe right half of Fig. 12 shows a lens blank edge at a distance d from a great polar circle: the left half of Fig. 12 shows a lens blank edge at a distance e from the same great polar circle. The long are tangent to the grinding surface of the tool represents the curvature to be ground on the lens blanks, the other" arc representing, in each case, the surface of the .unground blank. As the lens blank carrier is moved from right to left, along the axis of rotation'of the tool to the position shown inFig. 12, it is apparent thatfno partof :the lens blank having-its edge at distance erfrom the great polar circle would ever contact the grinding surface of the tool but the lens blank having its edge at distance d from the great polar circle has a portion of its surface which projects above the line of the grinding surface of the tool, hence that portion of the .lens blank would be ground ofl" as the carrier is'fed along the axis of rotation of the tool. If the lens blank were mounted so that its edge was on the great polar circle; 1. e, no spacing between lens blanks on the carrier then" that ed e of the blank would :be ground omple e y y he rou h rinding in -a tbe' ar i r moved along the axis of rotation of the grinding-tool and subsequent feeding of lens blanks to the grinding tool byrotation of the carrierwould not eflectany'further grinding on-this edgeof the lens blank, even by the central fine grinding ring, thus a portion of 91113 blank would not be fineground and hence thisrlens blank would have to be rejected. .It isiquite-a pparent, therefore, that ,it is advantageous to prowidewextra wide space between lens blanks on the carrier atone great .polar circle and, .imoreover, it is necessary to index the carrier to proper angularposition when it is inserted in the cradle as hereinafter noted.

Lens blank carrier 23 .issupported in .aislidably mounted cradle (Figs. 1,2, .3, ,4and 6 .in the following manner: Cradle-.31 substantially sphere ical .in form, splits in two halves at the equator, lower half 32 and .upper .half133 being hingedtoqgether by hinge pin 34 which lfits accurately. in bores in two aligned bosses 35 carried at the ends or brackets integral with upper half133, and also in "bores in four aligned bossesv 33 carried ,on .a bracket integral with.1ower"half"3 2 of cradlei3l. Also integral with lower half 32. of cradle 3| .is, a pair of long parallel bosses 13], each containing an accurate bore, the axis of which is parallel to that of the other'bore andboth axes lie 'in'a plane parallel to' the equatorial plane 'at' which cradle 31. is split. A pair of. parallel guide ,rodsjB'is a free but accurate sliding fit the bores bosses 31 and serves'to' support. slidably mounted cradle 3 Whfle 'I hav describ d c ad e3i i su tan t all he iea inform, it will b noted .fIQm i 14 tha len blan carrie 2. is contained within :cr de'tfll "and als tha cradle 1 1 x 51 s d hroue t e xsr ndins to l o suchppc itic that the polar axis of carrier "23 flies inthemedial plane of the grindingtool, Forthese reasons, lower half 'BZJ-and upper'half 133 or the cradle are flattened internally to provide suitablesupport for conical journal boxes :39 and M1, respectively, whereinlens blank carrier 23 is journaled, also, lower half and upper half33 of the oradie'have anexternal contour which is cylindrical inform over those areas which must be so formed to per-- mil; thecradle to slide into operating position within theygrinding rings. A cylindrical surface 4-1 and a flanged sea-t 42-arecontinuous overlower half*32 and'upper-half 33'of the cradle-and-are, respectively, anaccurate sliding lit in the bore and against-the face of flanged ring {4 attached to the casing enclosing the tool supporting shell, and serve to square, align and center the cradle within the grinding tool and thus properly position and fixedly maintain the polarpaxisgofi the lens blank carrier. aslensiblanks are-fed to the grinding tool by the rotation of. said carrier. A pinion 4'3, -meshing with equatorial-gear 21 on'ilens blank carrier23, isfixedon: one end of shaft. which is 'journaled in a bore in lower half :32 of the scradle and marries fixedly-mounted on its other end worm gear .(Fig .4). A worm .46, carried on shaft .41 meshes with worm ear '45. Through this gear train, lens blank .carrier' 23 is rotated, by power supplied by a small motor (not shown), to feed lens blanks to the grinding tool at optimum cuttingrate. v

A pair of brackets 48, integral with base F:i,gs. 1, 2 and 3) sup t a their nds osse ifl which are bored to fit snugly on hinge pin 50. tilting bracket 5| is bored'to fit snugly onhinge pin and carries'a pair of-bosses 52 containingparallel bores wherein parallel guide rods 38 :are a free sliding-fit. The other ends of parallel guide rods 38 are secured in bores in bosses 53 (Fig. :1) which are integral with flanged ring 14 :mounted on the housing enclosing the tool supporting shell. A control arm 54 is provided at one end with a boss bored to fit on hinge pin and at the other end with a boss bored to fit on pin.55 byn eans of which it is connected with .-lever .ar -m1 56'to which power is supplied lay-suitable means (not shown) to slide cradleSl containing lens blank carrier 23 from loading to grinding positionand vice versa.

Although I have not shown mechanism for. so doing, the operation of myequatorialdiamond milling generator caneasily, and should,. be made automatic except for loading the lens blank carrier in its cradle before .grinding andtaking-it out after the lens blanks are ground. Power .is supplied through .multiple M belts to pulley 1 to rotate the grinding tool atoptimu-m cutting speed. For loading, cradle 3!v isslid o'n parallel guide rods 38 all the-way to the right-(Figs. 1, 2 and 6) by operation of lever arm .56. and upper half 33 of the cradle is swung open to the right as illustrated .in Fig. .6. Lens b1ankcarrier -23, fully loaded with lens blanks to be groundoas shown in Fig. 5, is then dropped carefully into place in lower half 32 of the cradleandeq-uatorial gear 21 is meshed with .pinionI43 in indekedpo- .sition. Upperhalf 33.0f the cradle is .then swung baok-intoclosed positicn'and a snap ring 62hr threaded ring is placed over orscrewed .on the boss protruding from the. left side-of the cradle (Figs. .4 and 6-) thereby lockingthe two halves .of the cradle.securelytogether .and making-the polar conical jcurnalsonthe carrier lit accurate- ,ly in the polar. conical journal boxes-in thecradle.

It is to the noted here that conical type bearings will permit Jhingedopening .and closing 1 of .--the .cradle,.also'thi-s type of bearing is most-.satise factory 'for aligning the axis-centralizing the carrier inthe cradle andaccommodating thrust loads. 'By 1. operation of lever larrn 53. loaded cradle 3| is slid to-the lefton parallelg-uide rods .38, cylindrical surface -4 I. on cradle 3 l enters the .bore in flanged ring M, circulation ofboolant commences and those portions of alllenslblanks on the carrier which project beyond theccyli-n .dricalbore .of the grinding tool will ,be ground away as the cradle icontinues travelling toward the left and is finally- ,sto pedwhen hanged-seat 42 on thecradle makes complete contact with the outer faceof flanged ring l4. {Ifhestru es are such that the medial plane through the grinding t o w passes throu h- -the 'polarxaxis of the spherical carrier, i. :e., -the.; g-rind:ing;tool encircles the sphericalzcarri'er about;.a.-polar..,grgeat circle. The lens blank carrier. is s'nowiin correct position for grinding the lens blanks carried :thereon and power-:isapplied to equatorial gear .21, through the means described;toJrotatethe carrier .on its polar axis thereby feed-ingflens blanksto the grindingtool, the" lens blanks on the carrier at positions to the left of the medial plane through the grinding tool will be fed to the grinding tool from one direction and the lens blanks on the carrier at positions to the right of the medial plane through the grinding tool will be fed to the grinding tool from the opposite direction. Thus, the forces applied to the grinding tool in the axial direction, by feeding of lens blanks to the tool, constitute a couple and are balanced. The forces applied to the carrier, through rotative grinding by the tool, constitute a steady balanced torque, which tends only to rotate the cradle, not to displace it from its centralized position. It appears therefore, that, in this equatorial method of grinding, there are no unbalanced forces tending to set up vibration, hence lens blanks can be ground at maximum feeding rates and the ground surfaces will be free from chatter markings.

If the apparatus has been accurately constructed and is maintained in good-condition, one half revolution (180 degrees) of the carrier completes the rough and finish grinding of all lens blanks on the carrier, circulation of coolant is then stopped, the cradle is returned to its position at the extreme right on guide rods 38, the snap ring or threaded ring is removed from the projecting boss on the cradle, upper half 33 of the cradle is swung open and carrier 23 with its ground lens blanks is lifted out of the cradle and transferred to a cleansing bath, prior to being inserted in a cradle in a polishing generator. Thus, the grinding cycle is completed.

Interesting and thoroughly practical further applications of my improved equatorial diamond milling generators and methods may be made in ophthalmic lens manufacturing plants for volume production of toric surfaces. For instance, a special six curve lens blank carrier 51 (Figs. 14 and 15) may be used in a five curve diamond milling generator to rough and fine grind, successively and simultaneously, six-five curve toric surfaces in multiple. A six curve lens blank carrier cradle provided with proper driving gear arrangement for rotating special carrier 51 would be required, also it would be necessary to have a properly off set supporting and feeding structure for the cradle so the carrier 51 would be brought into position withrespect to five curve grinding rings as shown'in Figs. 14 and 15. For this type of surface grinding, a rough grinding ring 58 provided with coolant circulation channels as in Figs. 8 and 10, would be required, also a fine grinding ring 59 which is one half the axial width of fine grinding ring '9 (Fig. '7) used for generating spherical surfaces. It will be noted from Fig. 15, that the polar axis of special carrier lies in the plane of the left annular face of fine grinding ring 59 because it is the left edge of the abrading surface on the fine grinding ring which generates the final toric form on the surface of each lens blank as it passes thereunder. Subsequent polishing of the fine ground toric surfaces in multiple is described in my copending patent application for polishing generators previously referred to.

Whenever it becomes necessary to get at the grinding rings, the screws (Figs. 3 and 4) retaining flanged ring M in position on the tool supporting shell housing are removed and flanged ring [4 (Figs. 1 and 2) is pushed to the right as far as it will go, the guide rods 38 will slide through bores in bosses 52 until bosses 35 on the cradle contact bosses 52 and then the entire cradle supporting structure may be swung to upright position and out of the way as tilting bracket 5| swings through degrees on hinge pin 50. When work on the grinding rings is completed, the cradle supporting structure is swung back into horizontal position, flanged ring 14 is drawn all the way to the left and reseated on the tool supporting shell housing, retaining screws are inserted and screwed up tightly and the apparatus is again ready for grinding operations.

In ophthalmic lens manufacturing plants it has become standard practice to use lens blanks molded to 52 mm. diameter although first quality lenses are seldom, if ever,-required to center out to more than 44 mm. diameter. However, even with this wide latitude of 4 mm. on a side, many finished lenses now fail to meet first quality requirements because they will not center out to 44 mm. diameter: this because blanks are tipped when mounted for second side grinding or because of excessive prismatic grinding of blanks mounted around the periphery of large grinding shells. It is of interest to note how much needless surfacing of glass can be eliminated when lens surfaces are generated on blanks in such manner that the geometrical center of the lens is also its optical center. Since the area of a circle is proportional to the square of its diameter, the ratio of areas of 44 mm. and 52 mm. diameter blanks is equal to (44/52) or .717; so generator ground and polished lenses, if edged to finished diameter before surfacing, would save about 28 per cent of surface grinding and polishing. Moreover, lens blanks stuck together in sticks can be edged at much less cost than can finished lenses which must be edged singly. The use of edged blanks in my improved equatorial generator will represent further saving in cost of grinding rings and further reduction in grinding and subsequent polishing costs because an average of 25 per cent more lens blanks can be accommodated on a carrier. For example, on a six curve carrier, as shown in the drawings, sixteen 52 mm. diameter blanks are accommodated whereas twenty 44 mm. diameter blanks can be equally well fitted on a six curve carrier. This would represent 25 per cent more salable product from each generator. Edged blanks would permit further economies in operation: edged blanks seat better in carrier recesses and with less clearance, thus further eliminating factors tending to produc an inferior product.

In applying my improved equatorial diamond milling generator to lens manufacture, it is not necessary to have a special size machine for each curvature to be generated. For example, in making ophthalmic lenses from four curve" to ten curve, not more than six different machine sizes are desirable, intermediate lens curves being ground by using grinding rings of suitable bore in the next larger machine. For each desired curve to be generated, carriers are required to accommodate that curve but it will not be necessary to have a cradle size for each carrier size: in some sizes, a cradle may accommodate carriers varying in diameter up to a half curve." As has been stated hereinbefore, toric surfaces of various cylindrical powers may be generated on any spherical curve generator by substituting suitable grinding rings and providing the machine with the proper carrier, cradle and off set support for the cradle. These special items of equipment represent but a small extra cost.

Engineers skilled in the art of lens making will readily understand the principal advantages my get-meet improved equatorial diamond milling generator orrers most of which have been stated asobjects 'o'f' this invention. It is to be pointed out, how:- ever, that the greatest possible precision in lens grinding -is to be had from this machine and forth'e verysimplere'ason that there cannot'possibly'be any'roll-ing off at the edges ofthe ground surface: this because the grinding is done all ir ier and by '"grinding rings of precision form which do not "and cannot become deformed throughservie'e. Since there are ground lens blanks located "at both ends of many-diameters of the-spherical carrier, it is-a simple matter to measure curve diameter by micrometer-and kn'ow precisely, to a thousandth of an inch-or closer -if-defsira ble, jus't-whatcurvature has been generated on fthe lens blanks on each and every earner. These are prime advantages of the equatorial generating method and render it most them in another: "it might even be worth while to intermediate grind in a second generator before finish grinding i'na third machine. Should "this practice be followed in precision optics manufacture, it is obvious that only one-grain size of diamond grit 'will be used in each grinding "generator but multiple grinding rings will suu'be required and the functioning of the generator will be substantially the same as hereinbefore described. In other words, the equatorial generator will function equally well for any one "parti'cmar fineness of grinding if the multiple g'rindin'g"r ings shown in Figs. 7 and 9 all contain the samediamond grain size.

The structures 1 have illustrated and described .-represent, for the present, the preferred forms of my device. It is to be understood, however, that other mechanisms might be designed and constructed by those skilled in the art, for

performing the essential functions of the present structures, namely equatorial grinding of multiple lensblanksfmounted on a spherical carrier. The attached claims are drawn sufliciently broad tocover any and all devices of this character, also the methods of their uses, and it isthe intention that the claims be so interpreted.

Having thus fully described my improved equatorial diamond milling generator, also my multiple lens blank carrier and methods of operation to produce curved surfaces on multiple lens blanks mounted on a carrier, what I claim is:

-1 A diamond milling generator for combined rough "and/fine grinding of curved surfaces on a plurality of lens blanks in such manner that said plurality of lens blanks may be polished as a unit subsequent toigrinding, said diamond milling generator comprising a rotating tool unit suitably-supported, multiple grinding rings removany mounted in said rotating tool unit and arranged for combined rough and fine grinding,

successively and simultaneously, in either direction along the axis of said rotating tool unit, a multiple lens blank carrier of spherical form arranged for rotation on its polar axis, means whereby said carrier may be rotatably supported and brought into proper grinding relation with saldm'ultiple grinding rings means whereby-said carrier may be rotated on its polar ax-is'to feed lens blanks mounted on'said carriertosaid multiple grinding rings from two directions simultaneously, and means for rotating "said tool unit.

"2. An equatorial diamond milling generator c'o mprising, a base, a pair of aligned precision bearings suitably supported from said base, av-ro- "tat-in'g tool unit 'j'ournaled in said bearingamiiltiplegrinding rings remova'bly mountedin said ro tating tool unit and arrangedfor combined rough and fine'grinding, successively and simultaneouslyiyin either direction along the axis of rotation-of said tool unit, a multiple lens-blank-carrier of spherical form= arranged for rotation on fits polar axis; 'a cradle wherein said carrier is rotatably and-removably mounted, means for m'ovably supporting said 'cradle sosaid carrier amounted therein may be brought into prope'r grinding relation with said mmapiegrinding rings, means whereby said carriermay then be rotated on its polar axis to feed lens blanks to said grinding rings from two directions simultaneously, and means for rotating said tool unit.

3. A lens surface generating maehineeomprising, a base, a pair of aligned'bearings suitably supported from said base, a rotating'too'l unit journaled 'in said bearings, multiple grinding rings 'adjustably mounted in said rotating tool "unit and arranged for grinding simultaneously in'either directionalong-the axis of rotation as said "tool unit, a multiple lens blank -carrier-of spherical form arranged for rotation onits polar axis, a cradle wherein said" carrier is removably mounted for rotation, guide means for movably supporting said cradle so said carrier mounted therein may f be brought into grinding relation with said-multiplegrinding rings, means for accurately aligning, centering, squaring and securel-y supporting said carrier with respect to said grinding rings, means whereby "said carrier may then 'berotated on its polar axis tofeed lens blanks-to said multiple grinding rings from' tw'o directions simultaneously, and meansfor rotating said tool unit. i

4. A diamond milling generator compris'ing,- a base, a pair of alignedbearingssuitably supported from saidba'se, arotating tool unit journaledfiin said bearings, multiple grinding rings adjustabl-y mounted in said rotating tool unit and arranged for grinding simultaneously in either direction along'thelaxis of rotation of said toolunltpa casing enclosing said rotating tool unit, a multi- "ple lens blank carrier of spherical form arranged for rotation on its polar axis, -'a' split cradle of spherical formwhere'in said carrier is removably journaled,"guide means supported from said base *at one end and from said casing at theoth'e'r *endand arranged to movabl-y'support saidcradle so said carrier-mounted therein may be brought into grinding relation with said multiple grinding rings, means on said cradle engaging means on said casing to accurately align, center, square and securely support said carrier withrespect "to said grinding rings, means wherebysaid carriermay then be rotated on its axis to "feedlens blanks to said mu'ltiplegrinding rings from'two directions simultaneously, and means for rotating said tool unit.

5. A diamond milling generator comprising, a base, a pair of aligned bearings suitably supported from said base, a rotating tool unit journaled in said bearings, a grinding tool adiustably mounted in said rotating tool unit and ar- 15 ranged to grind simultaneously in either direction along its axis of rotation, a casing enclosing said rotating tool unit and securely supported from said base, a flanged ring attached to said casing having a bore centered on, and a face square to the axis of rotation of said tool unit, a multiple lens blank carrier of spherical form having conical journals on its polar axis, a split cradle of spherical form having its halves hinged together-and providedwith polar conical journal boxes wherein said carrier is journaled, guide means hingedly supported from said base at one end and fixedly supported in said flanged ring at the other end and arranged to movably supportsaid cradle so said carrier mounted therein maybe brought into grinding relation with said grinding tool, a cylindrical surface on said cradle entering the bore in said flanged ring to center said cradle on the axis of rotation of said grind- -ing.tool, a flanged seat On said cradle contacting overits entire area the face on said flanged ring to align, square, and support securely said cradle and said carrier journaled therein with respect .to said grinding tool, means whereby said carrier may .then be rotated within said cradle to feed lens blanks to said grinding tool from two directions simultaneously, and means for rotating said tool unit.

6. A diamond milling generator for precision toric surfaces comprising, a base, a pair of aligned precision bearings suitably supported from said base, a rotating tool unit journaled in said bearings, multiple grinding rings adjustably mounted in said tool unit and arranged for combined rough and fine grinding simultaneously and successively in one direction along the axis jof said tool unit, a multiple lens blank carrier of spherical form arranged for rotation on its .polar axis, said carrier being of somewhat smaller diameter than the bore of said multiple grinding rings, means whereby said carrier may be rotatably supported and brought into proper grinding relation with said multiple grinding rings, means .whereby said carrier may then be rotated on its axis to feed lens blanks to said multiple grinding rings from one direction, and means for rotating said tool unit.

7. A diamond milling generator for toric surfaces comprising a base, a pair of aligned bearingssuitably supported from said base, a rotating Ltool unit journaled in said bearings, a grinding tool having aninternal cylindrical abrading surface adjustably mounted in said tool unit and arranged for grinding in one transverse direction,- a multiple lens blank carrier of spherical "form arranged for rotation on its polar axis, said carrier being of somewhat smaller diameter than the bore of said grinding tool, a cradle wherein said carrier is rotatably and removably mounted,

off set means for movably supporting said cradle so said carrier mounted therein may be brought into proper relation with said grinding tool for generating toric surfaces, means whereby said carrier may then be rotated on its axis to feed lens blanks to saidgrinding tool transversely of said abrading surface, and means for rotating said tool unit.

. 8. In an equatorial generator, the combination of a multiple lens blank carrier spherical in form provided with conical polar journals and gear tor.

means whereby it may be rotated on its axis, and a. cradle somewhat in the form of a spherical shell wherein said carrier may be journaled, said cradle being split in two halves at its equator, said halves being hingedly connected so said cradle may be opened easily to receive said carrier, said halves each being fitted with a conical polar journal box wherein conical polar journals on said carrier enter with ease, means when said cradle is closed around said carrier for locking said halves to insure accurate alignment and precise fitting of said polar journals, and gear means on said cradle whereby said carrier may be actuated rotatively while journaled in said cradle.

9. In an equatorial generator provided with a grinding tool having an internal cylindrical abrading surface, the combination of a multiple lens blank carrier spherical in form and provided with polar journals and means whereby it may be rotated about its polar axis, a slidably mounted cradle somewhat in the form of a spherical shell wherein said carrier may be journaled, means whereby said cradle may be opened to permit said carrier to be quickly inserted and easily removed therefrom, means on said cradle for rotating said carrier while journaled therein, cradle supporting means, and means on said cradle and on said cradle supporting means whereby said carrier is accurately aligned, centered, squared and securely supported within said equatorial generator.

10. In an equatorial generator provided with a grinding ring having an internal abrading surface, the combination of a multiple lens blank carrier spherical in form provided with polar journals and means whereby it may be rotated, a slidably mounted cradle wherein said carrier may be removably journaled, means on said cradle for rotating said carrier while journaled therein, cradle supporting means, and means'on said cradle and on said cradle supporting means whereby said carrier is accurately aligned and securely supported within said equatorial genera- ARTHUR J. HOLMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Great Britain May 12, 1894 Great Britain Jan. 6, 1927 Great Britain Sept. 15. 1933 Number Number

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