GB2087092A - Multifocal lens comprising edge-fused lens portions - Google Patents

Abstract

A multifocal lens (10) is formed by positioning ground and polished elongate lens portions (12, 14) together with planar longitudinal edges thereof (16, 18) abutting each other, and fusing the planar abutting edges together. The multifocal lens (10) has little or no internal reflection or glare and hence is more comforatable for the wearer than prior art multifocal lenses. <IMAGE>

Description

SPECIFICATION Process for forming a multifocal lens and lens formed thereby The present invention relates in general to multifocal lenses and to the manufacture thereof.

Known multifocal lenses are subject to many drawbacks, such as glare, refelection off internal surfaces, small field of vision, and the like. One known process for forming multifocal lenses includes removing a piece of a single lens and replacing that removed piece with another lens portion. Such methods are disclosed in U.S. Patent Nos. 3,915,723, 1,996,442, 1,373,633,3,649,236, 3,563,057, 2,963,823 and 2,254,440. The replaced lens portion is formed of a material different from that of a single lens. In addition to the principal drawbacks of internal reflection and glare, the field of vision through the inserted piece is reduced from that field of vision otherwise available.

In anotherform of bifocal lens, the nearvision section is ground on the same piece of glass as the distance vision part. Disadvantages of this type of lens are; 1. The difficulty of making a sharp step in the line of seperation between two lens sections further creates the following disadvantages: a. highly specilaized equipment is required to manufacture such lenses; b. the manufacturing cost is thus relatively high; and c. step between two sections is not sharp.

2. When a near vision lens portion is ground on the bottom half of the distance vision lens portion, the top of the near vision portion will be a little below the top surface of the distance vision portion at the centre, and since the near vision lens portion has the greater degree of curvature, that lens portion will be considerably below the far vision surface at the outer edges of the bifocal lens. In order to leave these edges (on the near vision section) at a practical thickness, the entire lens must be made relatively thick and heavy.

Much precise grinding and polishing is required to finish known multifocal lenses, and accordingly, the manufacturing process is quite difficult and expensive.

The present invention provides a multifocal lens which does not suffer from these drawbacks of the prior art, and, in particular, exhibits little or no internal reflection or glare and hence is quite comfortable for a wearer. The multifocal lens of the invention includes lens portions which are ground and polished to correct respective vision defects. Each lens portion has longitudinal edges which are essentially planar. The longitudinal edges are ground so that those of a first lens portion are essential duplicates of those of a second lens portion and the lon gitudinai edges of the respective lens portions can be flushly fit and precision matched against each other. The lens portions are pressed together in longitudinal edge-abutting relationship with each other and are fused together at the abutting edges to form a unitary multifocal lens.

The present invention also includes a method of forming a multifocal lens. Each of a plurality of lens blocks is cut into arcuate elongate lens portions each having a pair of longitudinal side edges, a pair of end edges, an inside face and an outside face, and each lens portion is ground and polished to correct a vision defect.

Each longitudinal side edge of all the lens portions is ground so that they are all essentially planar and substantial duplicates of each other so that the longitudinal side edges will fit essentially perfectly flush when in abutting relationship. The ground and polished lens portions are interchanged and matched so that a plurality of vision defects can be corrected with a single matched set of lens portions.

The matched lens portions then are precision matched in edge-abutting relationship with each other so that a longitudinal side edge of one lens portion flushly abuts a longitudinal side edge of another lens portion. The edge-abutting lens portions are background so that all lens portions of the matched set have a common radius of curvature on the inner faces thereof.

The background edge-abutting lens portions are placed on a fusing jig and pressure is applied to force the edge-abutting lens portions together. The edge-abutting lens portions then are heated to a predetermined fusing temperature for a predetermined fusing time to the edge-abutting lens portions together at the abutting longitudinal edges to form a unitary multifocal lens. The predetermined fusing temperature then is decreased to a predetermined annealing temperature for a predetermined annealing time to anneal the unitary multifocal lens.

The multifocal lens so formed has a field of vision through the bottom half which is equal to that through the top half thereof. The lens halves which make up the lens can be positioned prior to fusing in a manner which most efficiently accommodates any step change in surface on the outside of the lens caused by the different radii of curvature of the two lens halves. The efficient accommodation of a step change in surface permits formation of light, thin multifocal lenses which have any noticeable line between lens portions minimized.

Both halves of the bifocal lens can be formed of the same material, and thus manufacturing costs can be reduced.

While the description of the present invention is directed mainly to a bifocal lens, it is to be understood that other multifocal lenses, such as trifocals, or the like, can be formed according to the same process without departing from the scope of the present invention.

The invention is described further, by way of illustration, with reference to the accompanying drawings, wherein: Figure 1 is an exploded perspective view of a grinding jig used in forming a lens of the present invention; Figure 2 is a sectional view along line 2-2 of Figure 1; Figure 3 is a perspective view of a fusing jig used in forming a lens of the present invention; Figure 4 is a sectional view along line 4-4 of Figure 3; Figure 5 is a plan view of a lens block used in forming a lens of the present invention; Figure 6 is a sectional view along line 6-6 of Figure 5; Figure 7 is a sectional view along line 7-7 of Figure 5; Figure 8 is a plan view of another lens block used in forming a lens of the present invention; Figure 9 is a sectional view along line 9-9 of Figure 8; Figure 10 is a sectional view along line 10-10 of Figure 8;; Figure 11 is an elevational view of a finished bifocal lens in accordance with one embodiment of the present invention; Figure 12 is a plan view ofthe bifocal lens of Figure 11;and Figure 13 is an end elevation ofthe lens shown in Figure 12.

Referring to the drawings, a multifocal lens formed according to the process hereinafter described is shown in Figure 11 and is denoted by the reference numeral 10. The bifocal lens 10 includes a top portion 12 suitably ground and polished for facilitating distance vision, and a bottom portion 14 suitably ground and polished to facilitate close work, such as reading or the like. The two portions are edge fused together along abutting edges 16 and 18 and both have a common inside radius 20 and individual outside radii 22 and 24, respectively. The two portions are formed in the same type of glass, and are edge fused together according to the process described below. Each of the portions 12 and 14 of the lens 10 isformedfrom a blank or block of lens glass, such as blanks 30 and 32 shown in Figures 5 and 8, respectively.The blocks 30 and 32 are ground and polished to the proper radii of curvature as indicated in Figures 6,7 and 9, 10 where the radius X in all figures corresponds to radius 20, and the radius Z in Figures 6 and 7 corresponds to the radius 22 in Figure 11, and the radius Yin Figures 9 and 10 corresponds to the radius 24 in Figure 11.

The preferred equipment used to form the lens 10 is shown in Figures 1 to 4, and attention is directed thereto. The lens blanks or blocks 30 and 32 are each cut into two halves, and these lens halves are indicated in Figures 1 to 4 by the reference numeral 50.

As shown in Figure 1,the lens halves 50 are all mounted on a grinding jig 60. The grinding jig is circular and includes a base 64 mounted onto a drive shaft 66 as by arboring or the like. The jig includes a central boss 70 located radially inward of the outer peripheral edge 72 of the base to define a mounting ledge 78 circumferentially disposed about the base 64. A plurality of elongate arcuate lens retainers 86 are attached to the central boss peripheral edge 88 by fasteners, such as cap screws 96, each inserted through a fastener accommodating hole 98 and threadably engaging a fastener receiving hole 100 defined in the boss edge 88 and aiigned with the hole 98. A plurality of arcuate spacers 106 are mounted on the ledge 78 to support the lens halves thereon.

As shown in Figure 1,the lens halves are mounted on the jig 60 to encircle same, and are all held on theo spacers 106 and in a position against the boss by the retainers 86. As shown in Figure 1, each of the lens halves has a pair of side edges 120 and 122, and a pair of end edges 126 and 128, and an outside surface 130 and an inside surface 132. The lenses are mounted on the jig 60 so that inside surfaces 132 engage the boss side 88 and one of the side edges, such as edge 120, extends above top surface 150 of the boss 70. The boss edge 88 can be slightly inwardly sloped as indicated in Figure 2 to provide better support for the lens halves, if so desired.

With the lens halves firmly mounted on the grinding jig 60, a grinding wheel 160 having an abrasive surface 164 is brought to bear against the exposed lens half edges 120 as shown in Figure 2. A gap 168 is defined between the surface 164 and top surface 150 of the jig to permit relative rotation of the grinding jig and grinding wheel.

The grinding process indicated in Figures 1 and 2 grinds the exposed lens half edges in a manner which makes all of those edges uniplanar, that is, edges 120' and 120" of the two lens halves 50' and 50" shown in Figure 2 are each perfectly flat with respect to each other and in the same plane. The lens half edges 120' and 120" thus are coplanar as viewed from end 126to end 128 and from face 130toface 132. The importance of the uniplanar nature of all of the lens half edges will be discussed below.

After grinding edges 120, the lens halves are removed from the grinding jig 60, inverted to expose edges 122 to the grinding wheel, and the process indicated in Figure 2 is repeated to grind the lens halves so that all of the edges 122 are also uniplanar.

The spacer blocks 106 and the ledge 150 are oriented and arranged so that once both edges 120 and 122 have been ground as above discussed, the edges 120 and 122 are essentially perfectly parallel with each other. The edges 120' and 120" are each essentially perfectly matched and substantially perfectly mateable with each other.

After completing the grinding process, a lens half 50' from the lens block 30 and a lens half 50" from the lens block 32 are selected and matched. The two halves 50' and 50" are placed in edge abutting rela-' tionship which is a flush relationship due to the perfect uniformity of the edges 120' and 120", and the inside radius of curvature is ground to form a flush and uniform inner surface las indicated in Figure 11.

The edge abutting lens halves are then mounted on a fusing jig 200. The fusing jig 200 is best shown in Figures 3 and 4 and includes a plurality of legs 202 supporting a horizontal supporting pallet 206. A backstop 210 is attached to upper surface 212 of the pallet 206 as by cap screws 214, or the like.

Afusing cradle 220 rests on top surface 212 of the pallet, and includes a creseed bolster block 226 having a planar bottom surface 230 and an arcuate top surface 232 which is breast-shaped to essentially match the curvature I of the inner surface of the lenses. A pair of gripping jaws 240 rest on the pallet on opposite sides of the bolster block. Each gripping jaw is L-shaped with a long leg 242 and a short leg 244. Bottom surface 246 of each gripping jaw rests on top surface 212 of the pallet so that the gripping jaw L shape is inverted. A shoulder 250 is formed at the juncture of the long and short legs and the upper surface 256 of the bolster block is received and accommodated by these shoulders. Each gripping jaw includes an outer back surface 260 which is presented outwardly of the fusing jig as indicated in Figure 3.One of the gripping jaw back surfaces abuts inner surface 262 of the backstop, and the other back surface is located adjacent the edge 264 of the pallet which is remote from the backstop. As indicated in Figure 4, the gripping jaw adjacent edge 264 can overhang that edge if so desired.

A clamp mechanism 270 is mounted on the fusing jig to retain the cradle in the assembled orientation shown in Figures 3 and 4 with the lens halves mounted thereon. The clamp mechanism includes an L-shaped swing arm 272 having a long leg 274 and a short leg 276 pivotally mounted on a bracket 278 by a pivot pin 280. The bracket 278 is affixed to the pallet 206 at edge 264 thereof. The short leg 276 has edges 284 and 286 which intersect to form a corner 290. The swing arm is mounted to pivot the corner 290 against the outer surface 260 of the gripping jaw located there adjacent, thereby forcing the cradle against the backstop, and the elements thereof together. A counterweight 294 is affixed to the end of the swing arm which is remote from the short leg thereof.The counterweight and the length of the long leg of the swing arm are selected so the clamp mechanism is self-adjusting to maintain substantially constant pressure on the cradle gripping jaws.

As best shown in Figure 4, the gripping jaws have inner surfaces 300 abutting the outer edges of the lens halves mounted on the cradle. The pressure exerted on the gripping jaws by the clamp mechanism therefore is transmitted to the lens halves to maintain an essentially constant compressive pressure on the lens halves.

The self-adjusting feature of the clamp mechanism permits a combination of lens movement during the heating and cooling cycles to which those lens halves will be subject. In this manner, an essentially constant compressive pressure is held on the lens halves during the fusing process.

Other forms of fusing jig can be used without departing from the scope of the present invention, however, any jig so used should maintain compressive pressure on the lens halves tending to maintain the abutting edges in contact during the fusing process, which pressure is essentially constant and accommodates lens movement during such fusing processes. In the preferred form, the fusing cradle is a ceramic material or aluminum oxide, or the like.

The multifocal lens thus is formed by edge fusing a pair of lens halves. Two lens blocks are each ground and polished. One lens block forms a distance correction and one block forms a near vision, or reading, correction. Each lens block is then cut in half. The edges of the lens halves are ground to be substantially flat, both transverse of the lens halves (that is, from the innerfacetotheouterface) and longitudinally of the lens half (that is, from one end edge to the other). The lens halves are turned over, and the other side edges are also ground to be substantially flat in both the transverse and longitudinal directions.

The edge ground lens halves are then matched, that is a distance correcting lens half is matched with a near vision correcting lens half, and placed in edge abutting relationship with each other. The substantilly flat edges facilitate this flush edge abutment of the lens halves.

Matched, edge abutting lens halves are then background. That is, the inner surfaces of the lens halves, e.g., surface I of Figure 11, are ground so the inner surfaces of the lens halves are perfectly flush and a smooth uninterrupted curve is defined for surface I.

The lens halves can be matched so the difference in curvature of the two halves is most efficiently handled. Thus, about one-half of the difference can be located at each end of the lens, thereby distributing the difference in curvature over the entire length of the lens and producing an overall lens in which a step change in surfaces due to differences in curvatures is distributed in the most advantageous man ner. This matching is best shown in Figures 12 and 13 where the distance vision lens portion is indicated by the indicator DV, and the near vision lens portion is indicated by the indicator NV. It is seen in these two figures that the step between the distance viewing lens portion and the near viewing lens portion is arranged between the centre of the bifocal lens and the edges thereof.This even distribution of a step change minimizes the line between sections noticeable to a wearer, and also makes it possible to make the lens thinner and lighter which is also an important advantage.

A bolster block of a fusing cradle is preferably coated with an anti-friction or anti-sticking agent, and the background, edge abutting lens has a place thereon. The cradle is supported on the fusing jig, and gripping jaws of the fusing cradle are clamped against the lens halves to hold those lens halves securely on the fusing cradle.

The cradle supported lens halves are placed into a heating means, such as a furnace, or the like, and enough heat is applied thereto to cause the abutting lens edges to fuse together to form a single, unitary bifocal lens. Just enough heat is applied to cause the abutting lens half edges to fuse together, as if too much heat is applied, the lense halves may run.

Satisfactory results have been obtained when the edge abutting lens halves have been held at between about 13600 and 1400"F (740"to 760"C) for about six minutes for a lens thickness of about 5-1/2 millimeters.

Once the lens half edges are fused together, the temperature of the heating means is dropped, and the bifocal lens is annealed. Satisfactory results have been obtained when a drop in temperature of about 200"F (95"C) is instituted, and the bifocal lens held at this lower temperature for about four hours. The fusing jig is then removed from the heating means, and the bifocal lens removed from the cradle.

It is noted that an alternative step in the above process includes heating only the abutting edges of the lens halves rather than the entire lens halves.

The entire lens halves may be heated to a temperature below the fusing temperature, then local appii- cation of heat to the abutting edges brings those abutting edges up to fusing temperature. Thus, for example, the lens halves may be heated to about 1200 F (650"C), then a quartz light, or a laser beam, may be focussed onto the abutting edges to heat those edges to about 1400"F (7600C) for a time sufficient to fuse those edges together.

The bifocal lens formed according to the preceding process comes out polished and finished on both the back and front surfaces and is easily and efficiently manufactured. Both halves ofthe lens are formed of the same type of glass, and thus many advantages are inherent therein.

Modifications are possible within the scope of this invention.

Claims (20)

1. An edge-fused multifocal lens, comprising a first lens portion which is ground and polished to correct a first vision defect and a second lens portion which is ground and polished to correct a second vision defect; each of the lens portions having longitudinal edges which are essentially planar and are ground so that those of the first lens portion are essential duplicates of those of the second lens portion and can be flushly fit and precision matched against each other; the first and second lens portions being pressed together in longitudinal edgeabutting relationship with each other and being fused together at the abutting edges to form a unitary multifocal lens.

2. A multifocal lens as claimed in claim 1, in which the first and second lens portions are focussed of the same type of material.

3. A multifocal lens as claimed in claim 1 or 2, in which the lens portions are oriented with respect to each other so that any discontinuity therebetween at the abutting longitudinal edges is evenly distributed over essentially the entire length of the edgeabutting lens portions.

4. A multifocal lens as claimed in any one of claims 1 to 3, in which the first and second lens portions have a common inside radius and different outside radii.

5. A multifocal lens as claimed in any one of claims 1 to 4, which is a bifocal lens incorporating two only of the lens portions.

6. A multifocal lens substantially as hereinbefore described with reference to, and as illustrated in Figures 11,12 and 13 ofthe accompanying drawings.

7. A method of forming an edge-fused multifocal lens, which comprises cutting a plurality of lens blocks into arcuate elongate lens portions; grinding and polishing each lens portion to correct a vision defect; grinding the longitudinal side edges of all the lens portions so that they are essentially planar and are substantial duplicates of each other; matching the lens portions so that a plurality of vision defects can be corrected with a single matched set of lens portions; precision matching the matched lens portions in longitudinal edge-abutting relationship with each other with a longitudinal side edge of one lens portion flushly abutting a longitudinal side edge of another lens portion; backgrinding the longitudinal edge-abutted lens portions to provide a common radius of curvature on the inner faces of all the lens portions; applying pressure to the longitudinal edge-abutted lens portions to force the lens portions together; fusing the lens portions together at their abutting longitudinal edges to form a unitary mul- tifocal lens; and annealing the lens so formed.

8. A method as claimed in claim 7, in which the pressure is applied to the lens portions and the lens portions are fused together on a fusing jig.

9. A method as claimed in claim 8, including coating thefusing jig with an anti-friction agent prior to placing the lens portions thereon.

10. A method as claimed in claim 8 or 9, in which the lens portions are placed on the fusing jig using a procedure invoiving a clamping step which is effected using a swing arm lever engaging the fusing jig.

11. A method as claimed in any one of claims 7 to 10, in which the fusing step is effected art a temperature of 13600 to 1400"F (7400 two 760 C) for 6 minutes.

12. A method as claimed in claim 11, in which the annealing step is effected at a temperature of 200so (75"C) below the fusing temperature for four hours.

13. A method as claimed in any one of claims 7 to 12, in which the fusing step includes heating the longitudinal edge-abutted lens portions to a temperature sufficient to fuse the lens portions together.

14. A method as claimed in any one of claims 7 to 12, in which the fusing step includes heating the longitudinal edge-abutted lens portions to a temperature below the fusing temperature of the lens portions and then raising only the abutted edges and the area immediately adjacent thereto to a temperature sufficient to fuse the lens portions together.

15. A method as claimed in claim 14, in which abutted edges are fused by focussing a quartz light on the abutted edges.

16. A method as claimed in claim 14, in which abutted edges are fused by focussing a laser beam on the abutted edges.

17. A method as claimed in any one of claims 7 to 16, including orienting the lens portions with respect to each other so that any discontinuity between the lens portions at the abutting edges is evenlydistri- buted over essentially the entire length of edgeabutting lens portions.

18. A method as claimed in any one of claims 7 to 17, in which the longitudinal side edges of a plurality of lens portions are ground essentially simultaneously.

19. A method of forming a multifocal lens substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

20. A multifocal lens whenever formed by a method as claimed in any one of claims 7 to 19.