US 3192676 A
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Description (OCR text may contain errors)
July 6 1955 l.. A. BUcKMlNsTER 3,192,676
LENS BLOCKS Original Filed Jan. 27. 1960 INVENTOR. LLOYD A. BUCKMINSTER United States Patent O 3,192,676 LENS ELCKS Lloyd A. Euckrninster, Geneva, FLY., assignor, by direct and mesu-o assignments, of one-half to Textron, las., Providence, Riti., a corporation of Rhode island, and one-half to American Qptical Company, Southbridge, Mass., a voluntary association of Massachusetts @riginal application dan. 27, 195i?, Ser. No. 4,95?, now Fatent No. 3,649,76o, dated Aug. 2l, i952. Divided and this application Aug. 2, i962, Ser. No. Zitl 4 Claims. (Qi. Sil-216) The present invention relates to the manufacture of lenses for spectacles, and more particularly to lens blocks for holding lenses so that they can be chucked in machines for generating and polishing their surfaces and for edge-grinding them. More specifically, this invention relates to lens blocks of the type disclosed in my copending application Serial No. 4,950, filed January 27, 1960, now Patent No. 3,049,766, granted August 2l, 1962; of which this application constitutes a division.
ln conventional processes for manufacturing an ophthalmic lens, a lens blank of molded glass is ground and polished on each of its two sides successively and then is ground on its perimeter or edge. Usually one side is concave and the other is convex; and the two surfaces have dierent curvatures so that the thickness of the lens varies at different points. The shapes and spatial relation of the two surfaces determine the desired optical refraction.
For the grinding and polishing operations, it is customary to secure the blank by means of an adhesive, such as molten pitch, to a lens block so that the lens may be chucked in the grinding and polishing machines. This block has, however, to be removed for edge-grinding the lens, and another block has to be used for this purpose. The block for holding the lens blank during surfacing has to be large enough to back up the glass of the lens over substantially its whole area to avoid breakage, 'while the block used for holding the lens blank during edging has to be small enough to clear the grinding wheel during the edge-grinding operation.
The principal difficulty in blocking an ophthalmic lens is in connection with a semi-linished lens, that is, a lens blank one side surface of which has already been ground and polished. The operation of grinding and polishing the unfinished side of the lens is the more exacting operation because the second to-be-nished surface must not only have the correct curvature, but must bear an exact and precise relation to the first-finished surface, in order for the lens to have the ophthalmic properties desired. rhe precise location of the second surface with respect to the rst may require either or both of two adjustments or settings, one called axis and the other called prisnr Setting for axis involves a rotation of the second surface with respect to the iirst, and setting for prism involves a tilting of the second surface with respect to the lirst. Adjustment for prism, as well as for axis may be achieved in the blocking operation, if desired.
The manufacture of ophthalmic lenses is further cornplicated by the fact that the center used in the surfacing operation may be different from the center used in the finishing operation.
ln any event, when surfacing a lens, the lens is ordinarily mounted on the prepared optical center. When edging a lens it may be necessary to use a different center called a mechanical center,in order to conform to the interpupillary distance called for on the lens prescription for the two lenses of a pair.
In blocking the lens blank, the semi-finished lens must be aiiixed to the lens block with its finished side against the head of the block in a known relation to the block,
in order that the opposite, unfinished side surface of the blank may be so nished as to bear the desired relation to the first-finished surface of the blank. For this purpose the first-finished surface of the semi-linislied blank may be marked in a suitable marking device, preparatory to blocking the blank.
The blocking operation proper follows the marking of the semi-ilnished blank. Various ingenious and complicated blocking devices are known, in which the blank is held by gripping means which permit the operator to adjust the blank manually until the ink marks, that have been placed on the blank, are visually aligned with indicia on the blocking device. (See, for instance, the apparatus disclosed in my above-noted copending application.) After the lens blank has been Visually aligned, the operator coats the block with molten pitch, and then aiiixes the blank to the block.
ln this way the finished surface of the semi-iinished lens blank will be precisely positioned with respect to selected surfaces of the lens block. The selected block surfaces are then used to align the lens block in the chuck of the grinding or polishing machine, thus indirectly aligning the lens blank with respect to the chuck, In this way, the relation of the second surface to be generated to the rstdinished surface is primarily determined during the blocking of the lens blank.
For these reasons, chucks have been used in recent years in which the position of the lens blank in the chuck is determined directly by registering pins in the chuck which engage against the fiished lens surface of the blocked lens blank. With these chucks, prism settings may be made directly in the chuck itself, and thus blocking is simplied. rl`hese chucks are, however, somewhat complex mechanically, and expensive.
Aside from the above-mentioned problems relating to the liking of the lens correctly on the lens block and in the chucks, there are other diiliculties attendant upon prior blocking practice. For instance, in prior blocking practice the blocking bodies are used over and over again. The result is that they get beat-up in use. This affects the accuracy of the centering of a lens `in the dilferent machines in which it is to be worked, with the result that it affects the accuracy of the lens itself.
Furthermore, as stated above, in manufacturing a lens or spectacles, it is necessary to have two different diameters of chucking surfaces, one for holding the lens during generation and surfacing, and the other for holding the lens during edging. The block for holding the lens during surfacing is too large for edging.
The practice heretofore has been to lay the lens out and to mark it, then to block it with pitch on the mounting block, then to surface it, then to take it olf the blocking bodx to measure it, then to remark it for the finishing operation, and then to effect edging. Each time that the lens has to be removed from a block, however, it entails the irksorne job of cleaning pitch olf the lens and off the block; and each time that a lens has to be blocked it involves the nasty job of applying pitch to the lens or block.
An object of this invention is to provide an improved lens block, and by means of which a lens blank may readily be checked in a grinding and polishing machine.
Another proiect of the invention is to provide a lens block which will enable the thickness of a lens to be measured while the lens is afhxed to the block.
Another object of the invention is to provide a twopiece lens block one portion of which is suitable for holding the lens blank during surfacing and generation, and a second portion of which is suitable for holding the lens blank during edging.
A further object of this invention is to provide a twopiece lens block, of the character described the portions dreams o of which are adapted to be individually removed from the blank following, respectively, successive stages of operation on the blank.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims when considered in cong'nnction with the accompanying drawing.
in the drawing:
FG. l is a bottom plan View of a lens lock made in accordance with one embodiment of this invention, and showing a semi-finished lens blank secured to the top of the block;
FG. 2 is a part side elevation, and part diametral sectional view of the lens blank and this block;
FIG. 3 is a view, similar to FIG. l, but showing a twopiece lens block made according to a modification of the invention, a semi-finished lens blank being shown mounted on the top of the block;
FIG. 4 is a part side elevation, and part diametral view of this lens blank and two-piece lens block; and
FIG. 5 is a front elevation of a lens blank showing in do* ed lines the outline of the finished. lens, indicating the positions of the optical and surfacing centers of the lens.
My above-noted copending application discloses the processes and apparatus for manufacturing lens blocks of the type claimed herein. By way of review, a lens b l; is held in position on top of a mold, and a heated lowmelting-point alloy is iiowed into the mold under one side of the lens blank, and is then allowed to cool adhering itself to the blank. The mold is shaped so that the alloy will cool to the shape of a lens block.
In the embodiment of this invention, which is illustrated in FIGS. 1 and 2, the molded block is of a type that will serve only during generating and polishing of the upper, unfinished side surface of the semi-finished lens blank. For edging,lthis molded block has to be removed, and the edging operation has to be carried out in the usual manner.
In the embodiment of the invention illustrated in FGS. 3 and 4, a small-sized block, such as is conventionally used for holding a lens blank for edging the blank, is first adhered to the semi-linished blank by pitch or any suitable adhesive. Then the blank, with this block axed thereto, is placed on top of a mold, and a melted low-melting point alloy is poured into the mold around the small-sized block to form the block that is used during generating and iinishing the exposed upper face of the blank.
in either case after the .molded block has served its purpose, it can readily be removed from the lens blank, as, for instance, by putting it into a small vise and squeezing on the block to cause it to break away clear of the blank. The removed block can be melted down again and used in molding another block for another lens blank. Thus, each time a lens blank is blocked by the process of the present invention, a new, clean, unmarred, accurate block is provided.
Referring now to the drawing, and rst to the ernbodiment of the invention illustrated in FIGS. l and 2, 11 denotes a lens block for holding a lens blank L during the surfacing of the latter. The block lll comprises a generally cylindrical head portion 12; and an integral, inverted, frusto-conical shank portion 13 projecting coaxially from the underface of the head portion. The upper face 14 of the head portion 12 is shaped in the molding process to conform to the shape of the underface 1S of the lens blank, to which the head is attached. It is a substantially smooth, concave surface.
The shank portion 13 of the block has three holes arranged in a line diametrally of the block. The center hole has a dome-shaped portion le, which is disposed coaxially of the block, and a reduced diameter portion 17 which extends from the inner, dome-shaped portion coaxially thereof to the concave surface i4. The other two holes also have dome-shaped portions, here denoted at .113, but they are not as deep as the center hole and do not communicate with the concave surface 14 in the head portion i2. They are radially spaced equal distances from the center hole, and are disposed at opposite sides of the center hole in diametral alignment therewith. They are identical in conliguration, but are of reduced diameter compared to the center hole. The wall of each portion i3, moreover, lares outwardly to provide a conical bearing surface 19 which surrounds the open end of a respective portion 13.
Preferably the material used for the lens block ll is a low melting point (for instance 136 F.), electricallyconductive alloy made, for instance, of a mixture of bismuth, lead, tin, indium and cadmium. As disclosed in my above-noted copending application, the block l is adapted to be molded directly onto the convex underside of the lens blank L to provide a means for chucking the lens in a surfacing machine. The two recesses in the block are adapted to accommodate two driving pins of the spindle or arbor of a generating or surfacing machine; and recess llo is adapted to receive the driving pin of a sphere surfacer, when a spherical surface is to be ground on a lens blank. The portion 17 of the central hole permits measurement of the thickness of the lens without removing the lens from the block. By engaging one jaw or feeler of a caliper with the underside i5 of the lens blank through hole i7, and engaging the other jaw or feeler of the caliper with the upper side 20 of the blank, the thickness of the blank can be read directly. Previously it was impossible to measure a lens once it had been blocked, unless the lens were tirst removed from the block.
After the operations on the blank have been cornpleted, the block lli may be readily removed from the blank by squeezing it between the laws of a vise, as described above, to cause the block to break away clear of the blank.
In the embodiment shown in FIGS. 3 and 4 numeral 21 designates a dual or two-piece lens block, one part of which is designed to be used during surfacing and iinishing, and the other part of which is intended for holding the lens blank during an edge grinding operation thereon. Block 21 comprises an outer portion 22 which is similar to the lens block 11 in the first embodiment in that it comprises a generally cylindrical head portion 23 from the underside of which there extends an integral, inverted, frusto-conical shank portion 24. Also as in block il, the shank portion 24 of member 22 is provided with three diametrically aligned recesses or holes. Two of these, 25, are identical and dome-shaped, and are equi-spaced radially on diametrally opposite sides of the central hole or recess which is denoted at 26 and which is of relatively larger diameter but also domeshaped. As in the case of block 11, the open ends of the recesses 25 are bounded by annular, conical bearing surfaces 27.
The upper face of portion 22 is again molded to conform to the shape of the underface of the blank L to which it is adhered. It has a smooth, concave upper surface 2S, similar to the surface id on block 11. However, unlike block il, the center of the cylindrical portion 23 of block 2]. is provided `with a coaxial, truncated conical recess in which there is secured a generally disk-shaped member 31 which has an upper face recessed at 32 that is surrounded by an integral, annular boss 33. The upper face 34.'- of boss 33 coincides with the concave surface 28 formed on the upper face of block portion 22, and with 5 spaced relation to the optical or mechanical center 37 of the blank. Apparatus for performing this operation is disclosed in my said copending application No. 4,950. Preferably portion 3l is made of a metallic or plastic substance which has a relatively low melting point, but one which is higher than that of the material employed in the surrounding portion 22. If the disk 3l is made of metal it will be relatively thick, approximately 1/8 inch; whereas if it is plastic, it can be very thin, approximately 0.005 inch. After the attachment of member 31 to lens blank L, a suitable mold (see the above-noted copending application) is employed to mold member 22 about member 3l and securely to the surface 35 on the blank L.
The portion 22 of the lens block is used for chucking the lens blank in a surfacing machine for generating and polishing operations. Following the surfacing operations, the portion 22 of the block, which is preferably made of the same material as block 11, and with a meltino point substantially lower than that of portion 3l, is then removed from the lens blank and from portion 3f., leaving the latter intact to permit the chucking of the blank L in an edging machine to complete the grinding of the lens blank around its marginal edge to a conguration such as shown by the broken lines at L in EEG. 5. Thereafter the member 3l may be removed from the lens blank by dissolving the pitch or other adhesive which has been securing it to the blank.
From the foregoing it will be apparent that applicant has provided a lens block which is relatively simple to manufacture, and which largely eliminates the errors due to damage to lens blocks by repeated use. Moreover, unlike prior lens blocks, it is possible, when using one type of block disclosed herein, to measure the lens-thickness without removing the lens blank from the lens block. In addition, applicants two-piece lens block 21 permits quick and precise chucking of the lens both for surfacing and edge-grinding operations.
While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any Variations, uses, or adaptations of the invention following, in general, theprinciples of the invention and including such departures from the present disclosure as come within known or customary practice in `the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention or the limits of the appended claims.
What is claimed is:
l. A lens block comprising (a) a centrally-disposed disc adhered directly to one side of a lens blank for holding said blank in an operating machine during one step in manufacture of the lens, and
(b) a body surrounding said disc and adhered directly to the same side of the blank in intimate contact therewith for holding the blank during a previous step in manufacture of the lens,
(c) said body being made of an alloy having a lower melting point than the material of said disc and than the lens blank.
2. A lens block for mounting a lens blank comprising (a) a first body having a concavedly shaped upper surface, and having a truncated conical recess formed therein centrally thereof,
(b) a second body seated in said recess and having a concavedly shaped upper surface disposed in the same surface of revolution as the Erst-named surface,
(c) said surfaces being adapted to be secured to and form a seat for a correspondingly shaped surface formed on one' face of a lens blank,
(d) said first body having in the end thereof remote from said surface a plurality of rectilinearly aligned recesses for receiving the driving pins of a machine for operating on a lens blank secured to said surfaces.
3. A lens block as defined in claim 2 wherein said first body is made of a material having a lower melting point than the material employed in said second body.
ft. A lens block as defined in claim 7 wherein (a) one of said plurality of rectilinearly aligned recesses is disposed centrally of said first body, and
(b) at least two other of said plurality of recesses are equi-spaced radially on opposite sides, respectively, of said one recess.
References Cited by the Examiner UNITED STATES PATENTS 2,603,922 7/52 McCarthy et al. 51-277 2,748,548 6/56 Hilsinger 51-216.2 2,859,568 11/58 VDantzic 51-2l6.2 3,118,198 l/64 Prunier 51-277 XR LESTER M. SWlNGLE, Primary Examiner.
lOl-IN C. CHRISTIE, Examiner.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,192,676 July 6, 1965 Lloyd A. Buckminster It is hereby certified that error appears in the above numbered patent requiring correct' e Said Letters Patent should read as corrected below.
Column 6, line 3l, for the claim reference numeral "7" read Z Signed and sealed this 7th day of December 1965.
SEA L) mest:
RNEST W. SWIDER EDWARD J. BRENNER nesting Officer Commissioner of Patents