US2306868A

US2306868A - Method for producing a one piece multifocal lens blank and lens

Info

Publication number: US2306868A
Application number: US336748A
Authority: US
Inventors: Frank E Duckwall
Original assignee: CONTINENTAL OPTICAL Co IN
Current assignee: CONTINENTAL OPTICAL Co IN; CONTINENTAL OPTICAL COMPANY Inc
Priority date: 1940-05-23
Filing date: 1940-05-23
Publication date: 1942-12-29
Anticipated expiration: 1959-12-29

Description

l -Dec v F. E. DL'JCKWALL 2,306,868

METHOD FOR PRODUCING A ONE PIECE MULTIFOCAL LENS BLANK AND LENS Filed May 25. 1940 Patented Dec. 29, 1942 METHD FOR PRODUCING A ONE PIECE MULTE'CAL LENS BLANK AND LENS Application May 23, 1940, Serial No. 336,748

S Claims.

This invention relates to a method for effecting an operation in the production of a one-piece multiiocal lens blank and lens having a noncircular inner near vision eld.

In the production of such lenses, it is customary to first surface a blank with a circular inner near vision field usually having its center substantially at the normal center or axis of the blank, and with a greater radius of curvature. The vaxis of the blank, as herein referred to, is the line passing through the centers of curvature of the inner and outer fields.

it has been proposed in providing a non-circular inner field, as distinguished from one-piece biiocal lenses of the Ultex type, to grind away or remove a portion of the inner field so that it becomes a part of the outer field, by means of a cam which guides the path of movement of the grinding and polishing buttons to conform with the desired non-circular curvature. This is disclosed in Letters Patent to Taylor, No. 2,097,001, issued October 26, 1937; Letters Patent to Houchin No. 2,087,687, issued July 20, 1937; and4 Letters Patent to Hubbell No. 1,928,538, issued September 26, i933. producing such a blank and lens, to first grind and polish a circular inner eld slightly depressed with respect to the outer eld. Following this method, the outer eld is ultimately polished down to merge with the depressed inner field.

It is found to be diicult in the commercial production of such blanks to effect a grinding and polishing operation which will completely remove a portion of the inner field and at the same time cause the outer field to smoothly merge with the remaining portion of the inner eld along the circular portion oi the boundary line. Thus, when the ground portion of the inner eld has been polished so that it merges indistinguishably into the adjacent portion of the outer field, the remaining portion of the outer field may, during this operation, be polished down below the adjacent surface of the inner field along the circular boundary line, which would leave an undesirable shoulder. On the other hand, if the outer eld were polished down just suflicient to cause a smooth merging or the surfaces along the circular portion of the boundary line, the ground away portion of the inner field may not have been sufficiently polished down to indistinguishably merge with the adjacent portion of the outer field.

The purpose of this invention is to provide a method which Will give a little more leeway or permit of greater tolerance in the polishing op- However, it is desirable in eration, whereby the inner and outer fields are so related that the ground away portion of the inner eld will be of the'same surface curvature and of surface continuity with the adjacent surface of the outer field, while there will still remain a slight depression of the remaining portion of the inner field with respect to the outer field along the circular portion of their boundary line. With this condition, the polishing of the outer field may then be continued with emphasis being directed toward lowering its surface by polishing just sufficiently to cause it to smoothly meet and merge with the surface of the inner field along such remaining circular portion of their separating boundary line.

This is accomplished by grinding and polishing the original circular inner iield slightly eccen tric with respect to the axis of the blank so that the portion which is to be ground away is less depressed relative to the outer field than the portion which will be bounded by the circular portion of the boundary line. Conversely, along the circular portion of the boundary line as it will appear in the finished blank, the inner field will be more deeply depressed and have a greater shoulder than that portion of the boundary line which will be ultimately removed. This relative arrangement oi the two surfaces will then permit of shallcwer grinding and polishing adjacent the removed inner field than will be required throughout the remaining surface of the outer field, for the purpose of allowing the two successive polishing operations above referred to.

The full nature of the invention will be understood from the accompanying drawing and the following description and claims:

Fig. 1 is a plan view of a lens blank showing the relative position of the ground and finished inner near vision eld with respect to the axis of theblank. Fig. 2 is a sectional view of the blank holder mounted on the spindle for rotation upon an axis oiset from the axis of the blank, with the polishing button applied thereto. Fig. 3 is an enlarged plan view of the inner eld indicating the position of the grinding or polishing button relative to the axis of the blank. Fig. 4 is a section on the line ri-fl of Fig. 3, showing the depth of the inner held greatly exaggerated. Fig. 5 is an enlarged and exaggerated sectional view of a portion of the blank showing a cam button secured to the inner field for controlling the grinding and polishing operation of the outer fled- Fig. 6 is an enlarged and exaggerated section of the blank with the cam button removed and indicating those surface portions of the blank to be ground and polished away to provide the finished outer field. Fig. 7 is the same as Fig. 6 showing the finished blank. Fig. 8 is a plan View of the finished lens.

Reference may be made to Letters Patent to Taylor No. 2,097,001, issued October 26, 1937, and particularly Figs. 1 to 4 and 9, as disclosing one method of producing a multifocal lens blank and lens.

A blank is first ground in the usual manner, and on the usual spindle, with its axis X concentric with aXis of rotationV of the spindle. is accomplished substantially in the manner illustrated in Fig. 2 with the eccentric extension l removed, and resulting ina blank I0 as shown in Fig. 1 having an inner near vision field ii indicated by dotted lines.

Thereupon said blank is further ground with its inner field I I eccentric of the axis. X, with its center positioned at Y, and surrounded by the outer distance vision field I2, as is illustrated in full lines in Fig. l. As shown in Fig. 2, this is accomplished by mounting the blank on the holder I3 in the usual manner, to be driven by the usual driving spindle I4, as is customary in the art.

For the purpose of this invention, the spindle I4, after the preliminary grinding, is provided with an eccentric extension I5 interposed between the spindle and the holder. Thus, the axial center of the holder and the spindle I-i' extends through the axis X of the blank. But by reason of the eccentric extension I5, the axis of rotation thereof, together with the hold-er and blank, will extend along the dotted line Y. Upon applying a grinding or polishing button i6 in the usual` manner, the inner field- Ii, upon rotation of the blank, will be reformed or enlarged with its center Y slightly offset from the axis of the blank as indicated at X and illustrated in Figs. 3 and 4.

As shown in Fig. 5, a cam button l'! is secured by cementing or otherwise, over a portion of the inner eld in the manner more fully set forth and described in said above-mentioned letters patent. This is for the purpose of guiding the grinding and finishing operation on the outer field during which a portion of the inner field ll is removed, leaving a non-circular inner field in the finished blank and lens.

By reason of the eccentric or off-center grinding of the inner eld, as'illustrated and greatly exaggerated in Fig. 6, the slightly depressed inner field is surrounded by a circular shoulder boundary line i3 which is of greater dep-th at the side distant from the axis X of the blank, as indicated at A than at the near side, as indicated at B. The purpose of grinding or finishing the inner field eccentricaliy, is to obtain this variation in depth of its depression for allowing more tolerance in the grinding and polishing of the outer eld for the reasons above discussed.

The next operation in producing the finished lens is to grind down that portion It! of the inner field which is exposed by the cam button l?, as shown in Fig. 5, until it takes the curvature of the outer eld and becomes substantially a continuation of the outer field surface I2. Thereupon, the whole of the outer field i2, together with said portion i9 of the inner field, is polished until the heaviei` shadedl portion, indicated by C in Fig. 6, is removed, which completely eliminates theshoulder indicated atB, while the.

This

reduced shoulder indicated at A remains. This is due to the eccentric relation of the inner field resulting in the shoulder B being of less depth than the shoulder A. The final step resides in the further polishing of the entire outer iield, removing that portion indicated at D resulting in the elimination of the remaining shoulder A. This latter step is designed to bring the surface of the non-circular inner field into smooth merging relation with the finished outer surface I2a about the circular portion of its boundary line, as indicated at i8, but leaving a flat shouldered upper boundary line 2d.

In view of the above, it may be considered that there are three operations in the grinding and polishing of the blank after the eccentric inner field l has been formed. The first operation is the grinding away of the exposed portion I9 of the inner field. The second operation is the polishing of the outer field until the ground away portion it merges therewith, eliminating the shoulder B. This leaves the inner field slightly depressed with a minute shoulder A about the remaining circular boundary line thereof. The third operation consists in polishing away the shoulder A left by this depression to eiect the smooth merger of the finished fields II and I2a along this boundary line I8, as illustrated in Fig. 7.

The invention claimed is:

l. The method of producing a one-piece multifocal vlens blank and lens consisting in mounting a concave blank upon a holder, rotating said holder and blank about an axis offset from the axis of the blank, applying a grinding and polishing tool to the concave surface of the blank adjacent and to one side of its axis of rotation, said grinding and polishing tool being formed to grind an inner near vision field with its center offset from the axis of said blank, whereby said field will be ground eccentrically of said axis to provide a greater depth of depression about the side farther from said axis than about the other side thereof, grinding and polishing away a portion of said inner field of lesser depth to the same curvature as the outer field, and polishing the outer field to smoothly merge with the inner field about the curved boundary line of its remaining portion.

. ishing tool to the concave surface of the blank adjacent and to one side of its axis of rotation, said grinding and polishing tool being arranged to grind an inner near vision eld with its center lying to one side of the axis of said blank whereby said field will be ground eccentrically to provide a greater depth of depression about the side farther from said axis than about the other side thereof, grinding away the portion of the inner field which is of lesser depth to substantially the same surface curvature as the outer iield,

polishing the outer field to effect surface continuity between it and the ground away portion, and continuing the polishing of the outer field until it smoothly merges with the remaining portion of the inner field about the curved portion 0f its boundary line,

3. The method of producing a one-piece multifocal lens blank and lens consisting in grinding and polishing a depressed circular inner near visionA field Within an outerdistanoe vision field and eccentrically of the axis thereof to provide said inner field with a depth of depression relative to said outer field greater on one side than the other, grinding and polishing away a portion of the said inner field on the side thereof having lesser depth to the same curvature as the outer field while leaving a surface elevation about the remaining portion thereof, and polishing the outer field to smoothly merge with said remaining portion of the inner field about the curved boundary line therebetween.

4. The method of producing a one-piece multifocal lens blank and lens consisting in forming a depressed inner field having a circular boundary line separating it from the outer field, grinding and polishing said inner field so that the depth of the depression about said boundary line will be greater on one side thereof than on the other, grinding and polishing the surface of the outer field and the portion of the inner field of lesser depth until said portion of the inner field is of the same surface curvature as the outer field while leaving a surface elevation and shoulder of said outer field about the remaining portion of the inner field due to said difference in depth, and thereafter polishing the outer field to reduce said remaining surface elevation until it smoothly merges with the remaining portion of the inner field along the remaining curved boundary line therebetween.

5. The method of producing a one-piece multifocal lens blank and lens consisting in grinding and polishing a circular inner near Vision field slightly depressed within an outer distance vision field, grinding and polishing said inner field with respect to the outer field to produce a depth of depression greater on one side than the other, grinding away a. portion of the lesser depressed inner field to substantially the same surface curvature as the adjacent portion of the outer field, polishing the outer field to effect substantial surface continuity between it and said ground away portion of the inner field while leaving a surface elevation and shoulder of said center field about the remaining portion of the inner field due to said difference in depth, and continuing the polishing of the outer field surface until it smoothly merges with the remaining portion of the inner field along the curved portion of its boundary line.

6. The method of producing a one-piece multifocal lens blank and lens consisting in grinding and polishing a circular inner near vision field slightly depressed within an outer distance vision eld, grinding and polishing said inner field L eccentrically of the axis of the blank to increased area for providing a depth of depression greater on one side than the other, grinding and polishing away a portion of the lesser depressed inner field to the same surface curvature as the adjacent portion of the outer field while leaving a shouldered elevation of the outer field in respect to the balance of the inner field due to greater depression thereof, and polishing the outer field to smoothly merge with the remaining portion of the inner field about the curved boundary line therebetween.

'i'. The method of producing a one-piece multifocal lens blank` and lens consisting in grinding and polishing a circular inner near vision field slightly depressed within an outer distance vision field, grinding and polishing said inner field slightly offcenter with respect to the axis of the blank to increased area for providing a depth of depression greater on one side than the other, grinding away a portion of the lesser depressed inner field to the same surface curvature as the adjacent portion of the outer field, polishing the outer field to effect a continuity of surface between it and the ground awa;r portion While leaving a shouldered elevation of the outer field in respect to the balance of the inner field due to greater depression thereof, and continuing the polishing of the outer field and said inner field portion until said outer field smoothly merges with the remaining portion of the inner field along the curved portion of its boundary line.

8. The method of producing a one-piece multifocal lens blank and lens consisting in mounting a concave blank upon a grinding and polishing head, rotating said head about an axis displaced from the axis of said blank, applying a grinding and polishing tool t0 the concave surface of the blank while rotating about its displaced axis to form a depressed inner near vision field with the center of said field offset from said axis whereby the depth of depression on one side of said field will be greater than on the other, grinding off a portion of the inner field on the side of less depth to the same surface curvature and continuity as the surrounding field of the blank while leaving a shouldered elevation of the outer field in respect to the balance of the inner field due to greater depression thereof, and polishing the surrounding field including said portion to smoothly merge with said balance of the inner field along the curved boundary line therebetween.

FRANK E. DUCKWALL.