US2545447A - Apparatus for grinding lenses - Google Patents

Description

March 20, 1951 G. A. CLEMENT 2,545,447

APPARATUS FOR GRINDING LENSES Filed June 27, 1947 4 Sheets-Sheet 1 INVENTOR. Geo/"ye H C/e/flem G. A. CLEMENT APPARATUS FOR GRINDING LENSES March 20, 1951 4 Sheets-Sheet 2 Filed June 27, 1947 March 20, 1951 G. A. CLEMENT APPARATUS FOR GRINDING LENSES 4 Sheets-Sheet I5 Filed June 27, 1947 INVENTOR. George A? (Va/Went my March 20, 1951 G. A. CLEMENT APPARATUS FOR GRINDING LENSES 4 Sheets-Sheet 4 Filed June 27, 1947 m R- o m H m W@ a ma S M w 0/ Q hm N a. 9m Km N\, 4 mm; M N N a w W Sm mm Qm mKNN Patented Mar. 20, 1951 UNITED STATES PATENT "OFFI'QE APPARATUS FOR GRINDING LENSES .George A..0lement,"Mount Vernon, N. Y., assignor to General optical Company, Inc., Mount Vernon, N.'Y., a corporation'of New York Application June .27, 1947,'Ser ial.No. 757,626

' 3 Claims. 1

This invention relates to the art of lens grinding, particularly. ophthalmic .or spectacle lenses. While the invention .isapplicable to both single and multiple vision lenses,.it-.-has. a special utility in connection with bifocalalensesuand will be described and explainedas it isapplied. in the production of such lenses, especially of the meniscus type.

Fused.- bifocal lenses .very generally havethe reading insert .or segment fused into a recess on the plus or convexvsidauand it is common commercial .practicefor the manufacturer .of the blanks to finishrlthisbifocal, or .plus .sideof the blank to the final lopticalisurface ,on one of the standard base curves. said to -.be :semiefinished and the .grinding.and polishing of thesurface on the other, or .minus side of the blank .to .satisfy the prescriptionis subsequently-done. The-blanksare commonly circular in form.

' The optical -.centerof the finished-lens, in the case of bifocals. especially, is commonly displaced'from the geometric-centerwof the blank, ordinarily being located below the horizontal meridian of the blank and to one side of the A vertical meridian so. as to .set, in the reading segment of the final .lens somewhat. The 10- .cation-of the optical center of-thefinished lens, being upon the axis of the lens, depends, .of course, upon the disposition of the centers-of the two surfaces and -hence uponthe attitude of the blank withrespect to the grinding axis during the generation-of the prescription curvature. The axis .of the lens is that intersecting line which includes the spherical-centers of the two-surfaces, andin spherical lenses is theonly line of observation whichis free from prism.

.As is well known, thecommonprocedurein the generation of the prescription surface "is to mark a spot on the finished-surface to denote the location of theoptical center, and then to chip or break off the edge of the .blank inone orvboth -meridians to bring-the-center equidistant from the ends of the meridians.v At that stage, the edge-of the blank is of. uneven thickness at the ends of the-meridians, and it isnecessary to present theblank to the grinding .tool in the subsequentv grinding .of the prescription or minus side so that theedgeoftheblank .becomes of even thickness at the .four points corresponding to theends of the meridians. This requires localizing of the grinding pressureiand frequent removal of the blank and measuring of the thickness -.at the meridianends with calipers. I

Such blanks are Such procedure is manifestly very slow and not only involves the loss of time due to. the ,frequent removal and measuring of theblank during the generatingprocess, but also the danger of damaging the finished surface due to the fine particlesof glass which result from the chipping lor -crumbing,,.as it is. called, adhering to that surface and scratching. it,land.there is also the .danger of the lensflying off the grinding tool and breaking in this operation.

The present invention. aims to improve on .thisprocedure. The need for chipping or crumbing the .edges of theblank before grindingthe second side is eliminated, as is theneed for measuring the edge thickness, .as the grinding. progresses. Thecinvention includes means for definitely and accurately locating the blank with .respectto the grinding tool, and retaining it in that-relative position until the generating operation isufinished.

.In accordance with the invention, .the semifinishedblank-ismounted on a rotative holder theaX-is of whichincludes the spherical or generatingv center of the grinding tool, and which has a supporting or locating spherical surface concentric with the finished surface of the blank, and adjustingithe blank. on that surface until theradius of the finished surface that coincides with. the desired optical center is brought into the axis of the holder. The blank is then secured inthisadjusted position andvthe grinding proceeds until thesurface on the minus side is generated. The common radial line of the two surfaces, which, as explained in my prior Patent'No-.,,1,46'7,308, is the line that determines the axis of the finishedlens, isin this case also the axis of generation.

The invention also .includes special apparatus to carry out the method-described. Preferably andmost conveniently, the holder has a marker, preferablyin the form of an axial post, in the center .of the sphericallocating surface to .denote' the axis of rotation, andthe blank is fixedly mounted on a ring which rests on thespherical surface .of the holder With the finished surface experience required to perform the operation successfully. The invention has other advantages and. novel features which will appear from the particular description of the embodiment illustrated in the drawings, which embodiment will now be described and the invention will thereafter be pointed out in claims.

Fig. 1 is a section on enlarged scale of a standard, fused bifocal, semi-finished blank.

Fig. 2 is a face view of the same with the location of the desired optical center indicated.

Fig. 3 is a diagrammatic view illustrating the problem in connection with a sectional diagram of the blank.

Fig. 4 is a similar diagrammatic view with diagrammatic representation of portions of apparatus associated therewith to show a simple solution of the problem.

' Fig. 5 shows diagrammatically a section of a ring and of a blank secured therein, with the problem indicated.

Fig. 6 is a diagrammatic view showing the elements of Fig. 5 mounted in operative relation with respect to a holder and grinder.

Fig. '7 is a section on the same enlarged scale of the complete mounting apparatus with a blank therein, the plane of the section being indicated by line 'I-'I of Fig. 8.

Fig. 8 is a plan of the apparatus on reduced scale.

Fig. 9 is a plan of the ring.

Fig. 10 is an exploded view in side elevation of the three members of the apparatus, to wit. the ring,'the chuck in which the ring is clamped and the holder in which the chuck is clamped.

A typical fused bifocal lens blank is shown in Figs. 1 and 2 in substantially double the normal size. The major blank member I is of crown or similar optical glass of a relatively lower index of refraction, while the minor blank member or segment 2 of glass having a higher index of refraction is fused into a spherical recess formed in the plus or convex side of the blank. To produce the semi-finished blank, this side, which is known as the bifocal side, is first ground and polished to a finished optical surface 3 of a selected base curve. It is to the grinding or generating of the prescribed curve on the second or minus side of the blank that this invention relates.

The meniscus, semi-finished blank has a molded, rough surface 4 on its concave or minus side, which, as shown, may be spherical and have its center of curvature on the geometrical central radius of the finished surface 3. Fig. 3 so shows it. The radial line 5 intersects the geometrical central point 0 of the surface 3 and also the spherical center 6 of the surface 3 and the spherical center I of the rough surface 4. In other words, both surfaces of the semi-finished blank are shown as symmetrical about the line 5.

It will now be assumed that it is desired to have the optical center of the finished lens located on a radius including the point :0 instead of the point 0 of the surface 3. Then the radial line 8 becomes the axis of the lens and must, of course, include the center 6 and the spherical center 9 of the surface Ill that is to be formed on the minus side of the blank. The final lens may be cut from the finished lens blank in any desired shape, for example, in the outline indicated by the dot and dash line in the plan view.

To accomplish the generation of the surface I0, the holder is rotated about an axis that includes the line 8. The simple diagram of Fig. 4

4 illustrates this. It is assumed that a holder II is rotatable about the axis of the post l2 which acts as a marker or indicator, and that the holder II has on its upper face an integral ring I3 coaxial with I2 and of uniform height. The spherical grinding tool I4 has its generating center on the axis of post I2 which is the axis of rotation, in this case at the point 9, the curvature of the tool being such as to generate the surface III.

The blank is placed on the ring I3 with its surface 3 down. The axis of the ring therefore includes the center 6 and sliding of the blank on the ring adjusts it about the center 6. Hence the radius of the surface 3 which intersects the point on the surface that happens to be in the axis of the post I 2, is the radius that corresponds to the axis of the finished lens and includes the optical center.

In Fig. 4, for example, the blank is disposed on the ring so that the radius 8, which intersects point x, is in the axis of the post I2, that is, the axis of rotation of the holder II. The line 8 is, therefore, the radial line that includes the optical center. To put it simply, what is done is to place the point x, which in practice will be designated by a dot made on the surface 3, directly over the end of the post I2, and with the blank secured in that position, the rotation of the holder and hence of the blank, with the minus side of the blank in contact with grinder I4, will generate the surface II) with the centers 9 and 6 in line 8 which is the axis of rotation.

It is obvious that in lieu of sliding the blank on a ring to get the desired optical center over post I2, it might slide in and be governed by a complementary concave surface in the holder. That, in effect, is what is done in practice. Figs. 5 and 6 show diagrammatically this feature of the commercial apparatus.

The blank I is mounted in a ring I5. In this case, the blank fits in the ring and is not adjustable with respect to it. This assembly of ring and blank is adjustably disposed on the holder II, which, in this case, has a concave spherical face I6 symmetrical about the post I2. This surface is concentric with the surface 3, its radius ll being equal to the radius I8 of surface 3 plus substantially the height of the ring I5.

Hence, when the ring slides on the surface I6, it slides about 6 as a center, and the blank therefore slides about 6 as a center, as is the case in Fig. 4. So all that it is necessary to do to get the desired location of the optical center of the finished lens, is to adjust the ring I5 until the point :1: comes over the post I2, lock the ring with screws I9, one of which is shown, and grind. In practice the generating tool I4 is itself also rotated on the axis 20, the tool being of a size to extend at least from the edge of the blank across the center of rotation of the blank in all angular positions of the blank, in order to prevent the formation of rings in the surface being ground.

In Figs. '7 to 10, inclusive, is shown the actual apparatus being used commercially. In addition to the ring and the element heretofore designated as holder, the apparatus includes a third element, termed a chuck which acts as the positioning holder for the ring. The advantage of having this third element is that it makes for easy replacement or substitution when a change occurs in the base curve of the blanks being ground.

The holder in this construction consists of a base member 2| that is mounted on a rotative seesaw? spindle 22 andiis"attached-theretoby a set screw 23. e-A:,chuckg;-member-. -24 grests upon. andis clamped to the holder 2|, and'itis the chuck that carries thesaxial post-. 12... Thechuckhas a machined bottom surfac'e that rests upon three studs 25-on the top face of the holder, the s'tuds being precisely machined toreceive and h'dld the chuck: in coaxial relation to theispindle.

The chuck is a eylindrical -member and. is clamped and pesitionedby three arcuate s'egments 26 upstanding from the peripherail edge of -the-holder."'The-middle portion of one of these segments, which, as in the other two, extends higher than the rest o'f the segment, ispivoted, as shownin- Fig. 7,-and-is-urged -out by a-s'pring 21 and is forced in by a screw 28 engaging in a tapped hole in the holder and operated by a handle 29. These parts are all designed and machined so that when the segments 26 are tightened the post I2 is in exact axial alignment with the spindle.

The chuck 24 is itself cup shaped and has a removable and replaceable circular bottom member 30, the surface I6 of which is a segment of a sphere concentric with the surface 3 of the blank. This surface l6 acts as the guide for the blank holding ring, as explained in connection with Fig. 6. The removability of the bottom member 311 permits of change of this member to keep the surface IS in agreement with the surface 3 when blanks having different base curves are bein treated.

The ring member 3| rests on the surface l6 and is secured in the chuck 24 in adjusted position. For this purpose the chuck is provided with three arcuate segments 32 upstanding from its peripheral edge, through each of which is tapped an adjusting screw, two of which, numbered 33, have knurled heads, while the third screw, numbered 34, has a flat head and is a thumb screw to be set up tightly to serve as the final lock for the ring.

The ring is a cup shaped member having a central opening in its bottom, and has a sharp axial lip 35 on its bottom face which rests upon the surface 16 and sharply defines the plane of contact. A removable annular member 36 fits in the ring and has a sharp top edge on which the blank rests. The ring has three upstanding arcuate segments for receiving and clamping the blank. Two of these, numbered 31, are integral with the top edge of the ring, while the third, numbered 38, is pivoted in a housing extension 39 on the ring and is controlled by a set screw 40 tapped through the housing and bearing against the member 38. A spring 4| urges the member 38 outwardly on its pivot so that the clamps open up as the screw is is retracted. ljhe segments 31 and 38 are faced with arcuate pads 42 of leather, fiber or the like to protect the edge of the blank when the clamps are tightened.

In use, a chuck member is chosen the bottom member 30 of which has a surface 16 of proper curvature to be concentric with the surface 3 of the blank to be treated. The point .r is marked on the surface 3 and the blank is secured in the ring. The ring is then set in the chuck and adjusted over the surface I6 until the point x is in register with the small axial extension of the post l2. The screws 33 and 34 are then set up and the ring is thereby locked in the adjusted position. The grinding may then proceed until the surface In is generated. Thus the axis of the finished lens is made to include the point While, as a rough measure, the radius I! is said'to be equal to the -radius il 8hplus the height ef-the i ring, strictly the :amount 'by which the radius l! exceeds the radius 'l8 f'ili lengthis a function of the effective height of the 'ring,': that is, of the axial distancefrom the plane of contact of the lip '35 with the surface I16 to the'plane of contact of the surface 3-with the sharp edge of the member 36 on which the blank rests.

' The grinder I4 is shown as having-:an alnnula'r spherical grinding surface. As is well. known; the annulus may be diminished iniwidth un'til' it'becomes so narrow that the cont'act-area is nomore in effect than -a circular line. The axis will'; o'f course, always include the center 9, which will' -be the 'spherical-center 'of the surface"generated'iby the grinder. Itwill -be understood; therefore, that --the term spherical herein when --applied to the grinder, is intendedto comprehend an annular tool of any width, and the terms spherical center and -generating- 'center as applied to the grinder, are intended to comprehend the point of intersection of the axis of the tool with the axis of generation, that is, the spherical center of the surface generated thereby.

It will also be understood that while in the above description reference has been made only to the generation of spherical surfaces on the minus side, the method and apparatus are equally applicable to the production of toric surfaces, and that the mounting of the blank is the same whether or not a cylindrical axis is introduced.

It is obvious that the method may be performed by apparatus differing in detail from that shown in the drawings and above particularly described, and that the invention is not limited to such details but only as pointed out in the following claims.

What is claimed is:

l. A mechanism for generating a surface on the minus side of a meniscus lens blank finished on the plus side, comprising a rotative spindle, a

holder mounted upon and rotative with said spindle, a removable chuck secured to the holder and having a concave spherical surface the spherical center of which is disposed on the axis of rotation of the holder, a ring adjustably disposed on said chuck surface, means to secure a lens blank on said ring with the plus side resting on the ring, means to secure the ring in adjusted position, the spherical center of the chuck surface being substantially beyond the supporting edge of the ring, and a rotative annular grinding tool applicable to the minus side of the blank and having its axis of rotation intersecting the axis of rotation of the holder.

2. A mechanism for generating a surface on the minus side of a meniscus lens blank finished on the plus side, comprisin a rotative spindle, a holder mounted upon and rotative With said spindle, a removable chuck secured to the holder and having a concave spherical surface the spherical center of which is disposed on the axis of rotation of the holder, a ring adjustably disposed on said chuck surface having its ends in parallel planes normal to its axis, an axial post extending from the chuck surface and into the ring, means to secure a lens blank on said ring with the plus side resting on the ring, means to secure the ring in adjusted position, the spherical center of the chuck surface being substantially beyond the supporting edge of the ring, and a rotative annular grinding tool applicable to the minus side of the blank and having its axis of rotation intersecting the axis of rotation of the holder.

3. A mechanism for generating a surface on the minus side of a meniscus lens blank finished on the plus side, comprising a rotative spindle, a holder mounted upon and rotative with said spindle, the holder havin thereon a concave spherical surface the spherical center of which is disposed on the axis of rotation of the holder, a ring having its ends parallel and normal to its axis and disposed on the said concave surface so as to be universally adjustable thereon, means to secure the ring in adjusted position on said surface, means to secure a lens blank on said ring with the plus side resting on the ring, the spherical center of the concave spherical surface on the holder being substantially beyond the supporting edge of the ring, and a rotative grinding tool applicable to the minus side of the blank and designed to grind a surface also centered on the axis of rotation.

GEORGE A. CLEMENT.

8 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 13,954 Scheurle July 27, 1915 978,764 Lincoln Dec. 13, 1910 1,224,169 Hice May 1, 1917 1,260,022 Paige Mar. 19, 1918 1,274,591 Quimby Aug. 6, 1918 1,282,037 Bugbee Oct. 22, 1918 1,436,626 Spaander Nov. 21, 1922 1,467,308 Clement et a1 Sept. 11, 1923 2,096,751 Martin Oct. 26, 1937

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