US1538813A - Bifocal lens - Google Patents

Description

M. A. LAABS ET AL BIFOCAL LENS Filed Sept. 22, 1922 F/GI - INVENTOR MAXA.LAA'BS HEW I v BY ATTORNEYS Patented May 19, 1925.

UNITED STATES PATENT OFFICE.

MAX A. LAABS AND HARRY W. HILL, OF SOUTHBRIIDGE, MASSACHUSETTS, ASSIGNORS TO AMERICAN OPTICAL COMPANY, OF SOUTHBRIDGE, MASSACHUSETTS, A VOLUN- TARY ASSOCIATION OF MASSACHUSETTS.

BIFOQAL LENS.

Application filed September 22, 1922. Serial No. 589,809.

To all whom it may concern:

Be it known that we, MAX A. LAABS and HARRY IV. HILL, citizens of the United States, residing at Southbridge, in the county of Worcester and State of Massachusetts, have invented certain new and useful Improvements in Bifocal Lenses, of whlch the following is a specification.

This invention relates to improvements in lenses and more particularly to a division of our application filed September 19, 1921,

Serial #501,650 and has reference to improved construction of bifocal lenses.

One of the principal objects of the present invention is the production of a novel and improved form of bifocal lens formed from two parts of glass in which the segment may be placed on the inner in place of the outer side, and in which the entire lens may be ground extremely thin without danger of damaging the segment of reading portion thereof.

A further object of the present invention is the provision of a lens of this character in which the size and shape of the segment may be largely varied as desired in the initial process of production, and in which wastage of glass in production of the lens is reduced to a minimum.

A further object of the invention is the rovision of an improved form of two part bifocal lens in which the position of the centers of the distance and reading portions in the finished lens may be. readily controlled and in'which the lens may be made of either monocentric or bicentric form as may be preferred.

Another object of the invention is the provision of an improved form of blank for producing lenses of this sort which shall be in what may be termed semi-finished condition when put out by the manufacturer, and in which the segment may if desired be left for further. grinding so that the prescription grinder may adjust the position of center of the reading portion according to his personal ideas in respect thereto.

Other objects and advantages of the present invention should be readily apparent by reference to the following specification taken in connection with the accompanying drawings, and it will be understood that any modifications in the specific details of construction or steps in production may be made within the scope of the appended claims without departing from or exceeding the spirit of the invention.

Figure I represents a plan View of a completed blank for a pair of lenses before separation. v

Figure II represents a sectional view as on the line IIII of Figure I.

Figure III represents a View similar to Figure VII represents a plan View illustrating the cutting out of an individual lens subsequent to grinding.

Figure VIII represents a view of the blank of Figure I split before grinding of the segment.

Figure IX represents a View of a method of grinding which may be employed to advantage in connection with the grinding of the blank of Figure VIII.

Figure X represents a perspective view of a monocentric typeof bifocal produced iigm the blank ground as shown in Figure Figure XI represents a-plan view of a pair of blanks such as used in Figure I showing most clearly the centering marks and flat edges molded on the initial blanks.

In the drawings, in which similar characters of reference denote corresponding parts throughoutthe several views, the numeral 1 designates the base blanks intended to form the distance portions of the bifocal lenses, these blanl sf's having the upper sur' faces 2 finished to the desired curve which may for example be a minus 6 curve, this being one standard .curve very widely used for the ocular side of meniscus lenses. These blanks, as indicated in Figure XI, are pref erably molded with a flattened port-ion 3 at one side and with a slight notch or nick as at L, the blanks when being fused being placed with the flat edges-in engagement with each other and the nicks corresponding to produce a diamond shaped aperture, as is indicated in Figure XI. 1 The lenses having been finished anglplaced to ether as indicated in Figure a large isc or segment portion 5 is then placed resting upon the curves 6, this disc being of circular form the glass may be sub ect to a heat insufficient to soften or affect the surface of the blanks 1S0 that their polished surfaces will be unaffected but the heat will prove sufficient to soften the member 5 and cause it to drop from the position shown in Figure II to the position shown in Figure III and firmly unite with the surface 2 making the parts integral one with the other.

We have found it of particular advantage in this connection to initially make the member 5 with its under surface flatter than the curve 2 and with its upper surface strongly curved to such a degree that after the softening of the parts the glass will be found to have bent to conform to the lower curve and securely unite therewith and a corresponding flattening of the upper surface will have taken place so that it will have dropped to substantially the curve which is to be subsequently produced thereon, thus minimizing the amount ,of grinding to be later performed. This also has'the advantage that a relatively thin edge is produced as at 18 which satisfactorily bears against the supporting blank and will very readily unite therewith while the heavier center portion will pull-itself down into close en- .gagement' with the glass. The advantage in mounting lenses on substantialy round blanks such as shown in Figure I resides in the fact that there is a space at each side as at- 9 where the segment is not supported, leaving an open passage under the segment through which the air can escape so there isv no danger of bubbles or the like interfering wlth the fusing and the-parts will fuse one tothe other. It is important that the disc 5 be properly positioned on the blanks 1.-

This is done by making a small drill spot, as at 10, in the disc 5 which is mounted directly over the diamond formed by the nicks 4. It will be understood that any other system of lining up the parts equivalent to this maybe employed so long as the disc is centered over the blanks so thefinal outline of the segment on the blanks will be the same.

In Figures IV and V we have illustrated a slightly different method of forming or uniting the parts. We make use of a -single large disc member 11 having the central kerf or groove 12 formed in its finished surface to afi'ord an outlet for the air. This groove is .sufliciently narrow but deep, so that the softening segment will come down against the face of the blank 11 but will not close up the groove. A permanent air outlet is thus provided at this point. This form of construction is particularly adapted to be subsequently ground as by the grinding tool 13 of Figure VI before the blank isseparated, the grinding being continued until the shoulder at 14 is brought down to within a few thousandths of an inch of the surface of the glass, when the reading portion of the lens is preferably considered finished. It is possible if desired to continue the grinding until the surface is brought even with that of the major blank so that it blends therewith or is brought slightly below the surface of the major blank, but we have found that best results can be line.

While the blanks can be mosteconomically surfaced two at a time and before-separation, if preferred the blanks may be first split as is shown by the individual blank in Figure VIII, and then subsequently ground either substantially parallel with the slirface of the discs or reading portion, as shown m Figure VI, or grinding the segment a??? at-an' angle, as is indicated in Figure leaving a higher shoulder at 15 than at the:

lower edge as at the point 16, the advantage of this being that a prismatic effect is introduced counteracting the natural prism of a non-bifocal lens, to the end that the center of the reading portion will be raised toward the geometrical center of the blank and if desired may be so positioned that the'lens as an entirety in its finished form will be amonocentric instead of a bicentric bifocal. This may be done either in the original process of manufacture or by the prescription grinder, as may be preferred, in the :so that there will be a prismatic balance in the two segments.

While we have referred to the segment and major portion of the blank as being formed from glass having different indices of refraction, such as crown and flint, it is to he understood that our invention is also useful in those instances where both the major and minor portions are the same, or substantially the same ndex of refraction,

- produced leaving a shoulder a few thousandths of an inch in height at the dividingunite therewith the segment through thealthough the segment is preferably of a glass having a lower softening point. This advantage resides in the fact that the major portion for a plurality of blanks may be satisfactorily provided With itsfinal surface on the bifocal side, and We may then heating action and subsequently have it ground and polish the segment only, a much distance or larger part of the blank in a circular zone or area about the central port1on.

We would also call attention to the fact that while We have referred to the parts as being fused together they might in some cases be united by a cement or heat actuated cement and that the heating action may i not necessarily be an actual fusion but and a segment secured to the major portion over said vent.

2. A multifocal lens blank comprising a said easier proposition in forming a lens of this sort than to have it ground and polish the major portion having a continuous curve formed on one side and having a vent formed therein and a segment secured to .the major portion on the side having a continuous curve and over said vent.

. 3. A 'multifocal lens blank'compr-ising a major portion having a vent therein and a segment fused to the major portion over the vent. 4. 'A multifoc'al lens blank comprising a major portion having a vent therein and.

a segment having an indexof refraction different from that of the major portion 1 fused over the said vent.

5. A multifocal lens blank comprising a major portion having a continuous curve formed on one side and having a vent therein'and a segment having an index of refraction different from that of the major portion fused to the major portion on the side having a continuous curve and over the said vent.

6. A multifocal lens blank comprising a major portion having a vent formed therein and a segment fused to the major portionover said vent, the outer surface of the segment having a different curvature than the adjacent surface of the major portion.

HARRY W. -HILL. MAX A. LAABS.

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