GB2046241A - Composite multifocal cane for use in the manufacture of bifocal lenses - Google Patents

Abstract

A composite multifocal cane rod (18), which can be sliced into a plurality of ophthalmic buttons (18x) for use in bifocal lenses, is manufactured by successive laydown from a continuous draw or successive moulding of individual cane rods. The cane comprises a first portion (S) of optical material having a selected profile including an interface line and at least a second portion (C) of optical material having a refractive index different from that of the first portion having an interface line complementary with the first mentioned interface line. The two portions are fused along the interface line. Figs. 6 and 9 show two of several alternative profiles. <IMAGE>

Description

SPECIFICATION Composite multifocal cane or segments and method of manufacture This invention relates to the manufacture of light refracting optical composite multifocal canes, rods or preforms for ophthalmic blanks, and a method of manufacture therefor.

Bifocal lenses are made by a great variety of methods. One such method which is commonly employed is distingusihed from others in that it employs a carrier produced from a glass, sometimes called crown, which is identical to that used for a major element of the lens, sometimes called the major. The crown is fused with a segment portion of another glass usually having a higher refractive index.

The carrier and segment are made by separate pressing and grinding steps and thereafter the elements are located in a refractory support and fused together so that an ophthalmic button is produced. The major has a recess formed in a front face thereof which recess is ground and polished to a selected curvature.

The button is processed with a rear face polished to match the curvature of the recess in the major and is located therein at a selected orientation. Thereafter the button and major are fused together and ground into the desired shape and size of a lens blank.

The many process steps in forming the segment, carrier, and major portions are time consuming and expensive. It has been discovered that composite cane may be produced which is formed of at least two types of glass material, one being identical with the carrier, and another formed of segment glass of a higher refractive index. The cane may be cut or sliced into buttons which may thereafter be ground and fused directly to the major.

According to the present invention, there is provided a composite multifocal cane adapted for use in the manufacture of bifocal lenses comprising: a first portion of optical material having a selected profile including an interface line, and at least a second portion of optical material having a refractive index different from that of the first portion having an interface line complimentary with said first mentioned interface line and fused with said first portion therealong, said first and second optical materials forming the composite multifocal cane.

In the accompanying drawings: Figure 1 is a schematic diagram of a continuous draw and laydown process for production of the composite multifocal cane of the present invention, Figure 2 is a schematic diagram illustrating the formation of an individual button from the rod or cane produced by the apparatus illustrated in Fig. 1, Figure 3 is a cross section along line 3-3 of Fig. 1 illustrating the profile of the composite cane and the mould in which it is formed, Figure 4 is a schematic diagram showing a different mould system for forming the composite multifocal cane with sequential moulding, and Figures 5 to 9 are end views of various profiles of composite multifocal cane which are produced by the methods described herein.

In Fig. 1 there is illustrated an apparatus 10 for forming composite multifocal cane 1 8 in which a delivery system 9, including delivery tubes 1 2 and 14, respectively, deliver streams of segment and crown glass S and C, via respective outlets 1 3 and 15, into a moving trough mould 1 6 passing under the delivery system 9. The crown glass C has an index of refraction which is usually identical to the major element (not shown) on to which buttons, such as those produced by the present invention, are fused for forming a fused multifocal lens.The moving trough mould 1 6 may be formed of successive sections or segments 16a, l6bor 16e moving along a horizontal line and driven by an endless conveyor belt or chain (not shown). The trough mould section 1 6b mates with adjacent sections 16a and 16e along seams 17 which seams are closed as the trough mould 1 6 moves under the delivery system 9.

In Fig. 3 there is illustrated an end section of the trough mould section 1 6 b along line 3-3 thereof. For convenience, the trough mould section 1 6b is simply a U-shaped member receiving the segment and crown glass S and C therein, which glasses are in a semi-molten viscous condition when they are layed down in cavity 1 6x of the trough mould 16. An interface 19 between the crown C and segment S glasses is formed by the successive laydown. The interface or boundary 1 9 is observable as the line, common in multifocal lenses, where glasses having different indices of refraction interact with light.The profile of the mould 1 6 may be different than illustrated, and while crown C and segment S glasses may be layed down in the preferred order shown, reversal of lay down is contemplated. Since the segment glass S tends to be less viscous than crown glass C, the preferred order of lay down shown herein, allows interface 1 9 of segment glass S to form flatly before lay down of crown glass C. If a formed orifice is used for delivery tube 1 5 crown could be formed with a shaped upper surface 21 and maintain such shape upon cooling by proper viscosity control.

In Fig. 2 there is illustrated a portion of the composite rod 1 8 formed in an apparatus similar to that of Fig. 1. A saw blade 20 may be used to cut the rod or cane 1 8 into individual blanks 1 8which may thereafter be ground and fused to the major in a conventional manner.

Fig. 4 illustrates schematically a variation of the present invention in which mould 26 including mould bottom 28, mould ring 30 and plunger 34 may be sequentially operated to first gob molten segment glass S into mould bottom 28. Thereafter plunger 34 is engaged to press the S glass as shown. The crown portion, not shown in Fig. 4, could be formed in an identical manner in a separate mould having an appropriate profile. Two formed pieces could thereafter be removed from respective moulds (e.g. see takeout valve 32) and later fused together to form composits rod 18.

Alternatively, the mould 26 in Fig. 4 could be enlarged to handle sufficient glass volume for multiple or sequential gobbing. Thus, once the segment glass S is gobbed and formed, the plunger 34 would be withdrawn and a gob of molten crown glass C (not shown in Fig. 4) could be deposited thereon. The same plunger 34, or another of appropriate profile could again be engaged to press the C glass fusing it with the S glass along interface 19, to form a rod 1 8. Takeout valve 32 located in opening 33 of mould bottom may be used to push out the fused glasses.

In Fig. 5 there is illustrated a trifocal button 23 which may be produced by the method and apparatus described in Fig. 1. A third delivery tube (not illustrated) would be appropriately located with respect to those outlets 1 3 and 1 5 illustrated. In Fig. 5, segment glasses S1 and S2 and crown glass C have different indices of refraction, and are formed with flat interfaces 1 9a between S1 and S2 and 1 9b between S2 and C into a rod similar to that illustrated in Fig. 2. Thereafter, the rod is cut into a button 23. Similarly button 25 illustrated in Fig. 6 is a trifocal blank utilizing curved interfaces 1 9e and 1 9d between the respective segment glasses S2 and S1 and the segment S1 and crown C.

In Fig. 7 there is illustrated a multifocal button 27 wherein the interface 1 9e between crown C and segment S is formed with curved portions or trough-like centre section 29 having a useful shape for bifocal lenses.

In Fig. 8 there is illustrated a button 31, which is a trifocal of the button 27 illustrated in Fig. 7, in which the segment glass S1 has a semicircular profile, crown C has a trough 29xfor receiving segment glass S2 therein interfacing at 19gwith the S1 glass and 19f with the crown C. A notch 24 may be formed longitudinally or axially along the button 31 in the S1 section to identify the portion of the bottom 31 which is the glass of a particular refractive index. At any rate, an appropriate indexing system might be integrally moulded into moulding apparatus or in delivery tubes of one of the forming devices described herein.

Fig. 9 illustrates yet another button 33, wherein the crown glass C is formed so that it surrounds the segment glass C along the interface 1 9 h. The interface 1 9 h has a lower profile resembling that of a semicircle and a horizontal upper profile. The shape of the blank 33 in Fig. 9 may be formed by a process similar to that shown in Fig. 1 with appropriately formed or shaped outlet orifices 1 3 and 15, etc. Note that in the Example, herein described, lay down order is reversed.

Thus, lower portion 34 of the blank 33 could be first layed down in moving trough 1 6 from outlet 1 3 of delivery tube 1 2. Thence an appropriately shaped stream of segment glass S could be delivered from outlet 1 5 of delivery tube 1 4. Thereafter another stream of crown glass C could be deposited on top to form upper portion 35 of crown C. There would be no line or interface between the lower crown glass 34 and the upper crown glass 35 since they would have the same index of refraction.

In Fig. 3, dimension D of rod 18 is a measure of its diameter. Dimension h is a measure of the distance from interface 1 9 to lower portion 36 of segment glass S. In bifocals having a straight line interface at lens 1 9 the conventional relation is h = 0.66D. In Fig. 5 the straight line trifocal button 23 also has a diameter dimension D. h1 is the distance of interface 1 9a between segments S1 and S2 to lower portion 36 and h2 is the distance of interface 1 9b of S2 and C to the same point. Conventionally, h2 = 0.66D and hl = 0.5D. In Fig. 6, h2 is curved interface trifocal button 25 is 0.75D and hl is 0.5D.In Fig. 7 and 8, h2 for respective interfaces 1 9e and 1spin trough-like multifocals are each 0.75D. hl in Fig. 8 for button 31 is 0.5D.

Dimensions for Fig. 9 are not given since it may take various shapes and forms. The dimensions noted above are exemplary only and are included for completeness of discussion and to illustrate that the present invention may be readily utilized with techniques and conventions accepted by the industry.

The operating temperatures and viscosities of the various glasses can be adjusted or tailored to provide the proper formation and fusion of the various segment and crown glasses as desired.

It should be further appreciated that, the present invention makes it possible to practically design a compatible series of glasses, so that, perhaps as few as ten different glasses may be produced in the different shapes described herein. Each glass has a selected index of refraction which makes it possible to mix and match indicies to produce any power lens in the range desired. Further by using such a system the major (not shown) need only be available in a few selected profiles as opposed to the present arrangements when as many as thirty-two profiles are required.

Claims (12)

1. A composite multifocal cane adapted for use in the manufacture of bifocal lenses comprising: a first portion of optical material having a selected profile including an interface line, and at least a second portion of optical material having a refractive index different from that of the first portion having an interface line complimentary with said first mentioned interface line and fused with said first portion therealong, said first and second optical materials forming the composite multifocal cane.

2. A cane as claimed in claim 1 adapted for formation into a plurality of ophthalmic buttons by slicing or sawing across a longitudinal axis of the cane.

3. A cane according to claim 1 wherein one of said first and second portions of optical material includes another interface line, the cane further including; at least a third optical portion having an index of refraction different from the first and second portions and having an interface line complimentary with said third mentioned interface line and fused therewith for the formation of the cane into a trifocal composite multifocal cane.

4. A cane according to any preceding claim wherein the first and second mentioned interface are planes.

5. A cane according to any one of claims 1 to 3 wherein the first and second mentioned interfaces are portions of a curve.

6. A cane as claimed in any one of claims 1 to 3 wherein the first and second mentioned interfaces are complimentary portions of a trough.

7. A cane as claimed in claim 1 wherein the first and second mentioned interfaces are portions of a cylinder.

8. A composite multifocal cane substantially as described with reference to the accompanying drawings.

9. A method of producing a composite multifocal cane comprising the steps of: laying down a first stream of optical material in a semi-molten viscous condition having a selected index of refraction, laying down at least a second stream of optical thermoplastic material in a semi-molten viscous condition, allowing said first and second stream to fuse at an interface therebetween.

1 0. A method as claimed in claim 9 wherein said first and second streams are layed down one over the other while in said semi-molten viscous condition.

11. A method as claimed in claim 10 further including the step of allowing said first and second streams to harden into a composite cane.

12. A method as claimed in claim 10 further including the step of: laying down a third stream of optical material in a semimolten viscous condition over said second stream, allowing said first and second streams to fuse, and allowing the composite of three optical materials to harden into a composite cane.

1 3. A method as claimed in claim 12 further including the step of: continuously drawing the first, second and third streams during said laydown step.

1 4. A method as claimed in claim 9 including the step of: forming the optical materials prior to lay down with selected profiles for the desired interfaces.

1 5. A method as claimed in claim 9 further including the step of establishing a compatible series of glasses having selected indices of refraction, and producing various multifocal cane composites having different powers by selecting various ones of said glasses in said compatible series in selected groups of at least two glasses.

1 6. A method of producing composite multifocal canes substantially as described with reference to the accompanying drawings.