US3117396A

US3117396A - Lens grinding apparatus and method

Info

Publication number: US3117396A
Application number: US83297A
Authority: US
Inventors: Ernest T Dalton
Original assignee: American Optical Corp
Current assignee: American Optical Corp
Priority date: 1961-01-17
Filing date: 1961-01-17
Publication date: 1964-01-14
Anticipated expiration: 1981-01-14

Description

Jan. 14, 1964 E. -r. DALTON 3,117,396

LENS GRINDING APPARATUS AND METHOD Filed Jan. 17, 1961 2 Sheets-Sheet l IN VENTOB ERNEST 7.' DHLTON Jan. 14, 1964 E. T. DALTON 3,117,396

- LENS GRINDING APPARATUS AND METHOD Filed Jan. 17, 1961 2 Sheets-Sheet 2 I N VE N TOE ERNEST 7T DALTON QTTOE'NEY United States Patent 0 3,117,396 LENS GRINDING APPARATUS AND METHOD Ernest T. Dalton, Southhridge, Masa, assignor to American Optical Company, Southbridge, Mass., a voluntary association of Massachusetts Filed fan. 17, 1961, Ser. No. 83,297 6 Claims. (Cl. Si -33) This invention relates to the grinding of lenses or like articles and has particular reference to improvements in apparatus and method for grinding compound surface curvatures on such articles.

In providing lens blanks or the like with compound surface curvatures by grinding operations, considerable dithculty has been experienced heretofore in forming the curvatures accurately enough and, at the same time, to such a texture of finish as to permit said surfaces to be optically polished without an intermediate step of truing or otherwise fining the ground surfaces.

This invention relates more particularly to the grinding or, generating by grinding, of true toric surfaces on lens blanks which surfaces are of such contour and texture of finish as to be adaptable to direct finishing by polishing. The reference herein to a toric surface is intended to mean a surface having a compound curvature which, when measured along a first major meridian, is of a different predetermined radial dimension than when measured along another meridian normal to and passing through said first meridian. The use of the term true toric surface is intended to mean a surface of the above character whose curvatures, when measured along the said meridians, are each entirely free of elliptical errors or other inaccuracies in radial dimension and are, therefore, precisely of the intended radii of curvature from edge-toedge along said meridians so that, when directly optically polished to the curvature generated thereon, the resultant toric surface of the lens blank will be well within the tolerances of precision required by the optical profession.

In generating toric surfaces on lens blanks by conventional practices through the use of the so-called universal cupped tools and their usual associated machinery wherein, by angular adjustment of the efiective abrading edge of the tool relative to a lens blank, various different curvatures may be selectively applied to the lens blank in the direction of one of its meridians, the well-known and inherent errors of ellipticity cannot be avoided. These errors are such that, along at least one of the major meridians of the egnerated lens blank, an undesirable condition of ellipticity is present which increases in severity in directions from the center of a lens blank toward the marginal portions thereof. Since elliptical errors of curvature in finished lenses do not produce accurate prescriptive powers along the major meridians of the lenses, it is essential that the curvatures along said major meridians be of constant radial dimension from edge-toedge. in view of the fact that these elliptical errors cannot be tolerated in finished lenses, it has been the practice to surface the lens blanks after generation and thereby remove elliptical and/or other errors of curvature prior to polishing. This is most commonly done with loose abrasives placed between the lens blank surface and a preformed lap initially having a true toric surface which is contrageneric to that desired of the finished lens blank. Such an intermediate truing operation is disconcerting to lens manufacturers because of its expense and consumption of time and further because of its limita tions in accuracy. As it is well known in the art, the forming of toric surfaces by lapping with loose abrasives is accomplished by, in effect, moving the lens blank in substantially full surface engagement over the preformed lap in the directions of both the major meridians of the toric surface. Such a compound motion causes the abrasive material to abrade the lens blank but, at the same time, it produces an abrasive action or wearing of the lap with the result of causing disfiguration of its initially true toric surface. The lens blank, at best, can only assume the surface shape of the lap and lap wear resulting from abrading with loose abrasives produces inaccuracies of surface curvature upon such lens blanks. Furthermore, truing operations require a great many laps, one for each of the multitude of different toric surfaces presently needed in the optical profession and expensive machinery as Well as periodic retrain-g of the laps and the use of messy and befouling abrasive slurries.

In an attempt heretofore to avoid surface truing operations such as mentioned above, various techniques of grinding toric surfaces with preformed types of abrasive tools have been attempted wherein barrel or similarly shaped tools having continuous toric shaped abrading surfaces are passed across a lens blank surface to produce a milling effect thereon. This type of grinding has left much to be desired since it is a straight out operation wherein no break-up motion exists or can be made to exist between the work piece and tool. In the absence of any break-up motion during abnading, unavoidable irregularities such as protruding or receding abrasive particles or the like on the abrading faces of the tools produce ridges or grooves across the lens blank surfaces which, in most cases, cannot be subsequently polished-out or which, at best, render the polishing operation extremely difficult, lengthy and usually unsuccessful in instances where extreme accuracy and high polishes are required as in the ophthalmic art. Therefore, while milling operations with barrel-like tools tend to overcome some of the difficulties relating to elliptical errors, they do not produce surface textures suitable for direct optical polishing and, in general, do not obviate the need for an intermediate surfacing or fining operation between grinding and polishmg.

Accordingly, it is a principal object of the invention to provide improved apparatus and method for generating, by grinding, true toric surface curvatures upon articles such as lens blanks or the like with such accuracy of curvature and texture of finish as to permit direct optical polishing of said generated surfaces and 'with no intermediate truing or fining operation being required.

Another object is to provide apparatus adapted to generate true toric surfaces and which, when in operation, produces the effect of a break-up motion characterized to provide the abraded articles with surface textures of an all-over uniform nature suitable for direct finishing by conventional optical polishing operations.

Another object is to accomplish the above through the use of apparatus embodying a rotatable grinding tool having a cup-shaped forward configuration with a preformed curved grinding face portion on the edge of the rim of the cup which is rotated and fed across the work piece with the rotational axis of said tool and the general direction of feed thereof across said work piece angularly re lated to each other at all-times during operation of said apparatus.

Another object is to feed said work piece and tool, one transversely relative to the other along an arcuate path swung about an axis disposed at substantially right angles to the axis of rotation of said tool.

Another object is to provide said face portion of said tool with a true spherical curvature having a radial dimension precisely equal to that desired along one major meridian of the finally ground article.

Another object is to produce, by use of a tool of the above-mentioned type and the particular axial positioning thereof relative to the direction of feed across a work piece, a combined rubbing and wiping grinding action along progressively changing paths over the surface of the work piece which action will be referred to hereinafter as a break-up motion.

Another object is to provide by means of said break-up motion, an effect which in addition to producing a superior surface finish upon a work piece, provides the tool with an automatic shape-correcting and/ or shape-retaining feature such as to accommodate and correct for slight tool irregularities resulting from protruding abrasive particles or the like on its effective grinding face and wherein, during operation, said tool will have a tendency to become automatically shape-corrected and freed of such irregularities wherever they may initially exist and thereafter retain its true form of curve with a minimum effect of wear.

Another object is to provide tools of the above-mentioned character which have reclaimability and may be readily dressed when necessary to compensate for wear resulting from extended periods of use.

Another object is to provide an abrading tool of the above character having an effective grinding face portion of such an outer diametrical dimension as to ride over and beyond the edges of a work piece being ground thereby while, at the same time, being so arranged and applied to the work piece as to have all portions of said grinding face repeatedly, at one time or another, in engagement with said work piece during grinding so as to eliminate wear differentials upon the said tool face and, as a result, obviate the common causes of marginal and other errors of curvature upon the work piece.

Another object is to provide means and method for producing true toric surfaces upon lens blanks or like articles with a minimum of operational steps and processing time and with apparatus which is uniquely simple in structure, foolproof, dependable in duplication of its operation and highly desirable for use in mass production operations.

Other objects and advantages of the invention will become apparent from the following description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective diagrammatic illustration of a lens blank having a true concave or negative toric surf-ace formed thereon in accordance with this invention;

FIG. 2 is a perspective diagrammatic illustration of a lens blank having a true convex or positive toric surface also formed in accordance with the invention;

FIG. 3 is a diagrammatic plan view of apparatus which is shown as being arranged to produce lens blanks of the type shown in FIG. 1;

FIG. 4 is a fragmentary cross-sectional view taken substantially along line 44 of FIG. 3 looking in the direction indicated by the arrows;

FIG. 5 is an enlarged face view of a grinding tool such as is shown in FIGS. 3 and 4;

FIG. 6 is a schematic illustration of the tool and work piece relationship shown in FIG. 3;

FIG. 7 is a view similar to FIG. 6 schematically illustrating the tool and work piece arrangement required for the forming of lens blanks of the type illustrated in FIG. 2; and

FIG. 8 is a diagrammatic illustration of means and method for optically polisln'ng work pieces having surface curvatures ground thereon in accordance with the invention.

Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the several views, it will be seen that in FIGS. 1 and 2 lens blanks 10 and 10' respectively have been illustrated as having each of their respective surfaces 12 and 12' formed to a toric shape in accordance with the practice of this invention. The lens blank 10 whose surface 12 is concave will be referred to hereinafter as a negative toric lens blank and the lens blank 10' whose surface 12' is convex will, accordingly, be referred to as a positive toric lens blank.

It will become apparent hereinafter that the abovementioned lens

blank surfaces

12 and 12 are each generated directly to a true compound curvature such that when measured along their respective major meridians B and C or B and C their curvatures will be precisely of the desired radial dimensions and substantially entirely free of the well known elliptical errors or other common inaccuracies.

As in the case of all toric surfaces used in the ophthalmic art, the curvature measured along the meridian B in FIG. 1 or B in FIG. 2, being weaker in power or of a longer radius of curvature than that measured along the meridian C in FIG. 1 or C in FIG. 2 will be referred to hereinafter as the base curve of the surface 12 or 12' and the curvature in the direction of the meridian C or C will be referred to as the cylinder curvature, it being stronger in power or of a shorter radius.

Referring now to FIG. 2, it will be noted that the major meridian B indicating the base curvature of the surface 12' is illustrated as being vertically disposed as opposed to the horizontal direction of the base curve meridian B of FIG. 1 and the major meridian C indicating the cylinder curvature in FIG. 2 is disposed horizontally since said meridians are taken at right angles to each other. It will become apparent hereinafter that this effect of reversal in the directions of the major meridians of the

lens blanks

10 and 10 is simply the result of the particular procedures followed and given by way of example in the generation of the plus and negative

toric surfaces

12 and 12. The lens blanks 10 or 10 when put to use after being optically finished are arranged to have their base and/or cylinder meridians oriented in accordance with the particular prescriptive requirements of the user. This is accomplished in the well known manner of cutting finished lenses from the lens blanks whose peripheral contours are so controlled in position or orientation relative to a selected direction of the major meridians of the

toric surfaces

12 or 12 and located relative to the point of intersection of said meridians (the optical centers of the respective lens blanks) as to position the resultant lenses centrally before the eyes with their major meridians of curvature so oriented as to suit to the needs of a user when said lenses are mounted in holding means such as spectacle frames or the like.

In accordance with this invention, the toric surfaces 12 and 12' are each generated upon the

respective lens blanks

10 and 10 with a cupped-type grinding tool 56 having an effective abrading face portion accurately preformed or dressed to a true spherical shape which is precisely of the curvature desired to be formed on the particular lens blank in the direction of a first of its major meridians While the curvature in the direction of the opposed meridian of the particular lens blank is generated by swinging the tool along an arcute path transversely in a direction normal to said first meridian and swung about a pivotal axis radially spaced from the effective abrading face of the tool at a distance equal to the radius of curvature desired on said lens blank in the direction of its second or opposed meridian.

It is pointed out that the cupped-type grinding tool 56 is rotated about its axis to produce a grinding action on the particular lens blank being ground and the axis about which it is swung across the lens blank is disposed at right angles to the axis of rotation of the tool.

The effective abrading faces of the grinding tools used herein are preferably of the diamond impregnated or diamond charge type which are well known for their superior cutting action and wearability.

In FIGS. 3 and 4, apparatus for generating the negative toric surface '12 upon the lens blank 10 is shown diagrammatically as embodying a main supporting section or base 14 having a guideway 16 extending along the major portion of the length of its upper surface and upon which is mounted a first slide 18 in dovetailed fashion or otherwise arranged to be slidable axially along the guideway 16 and locked thereto when located at a desired position by means of a suitable set screw arrangement or a conventional type cam lock which is diagrammatically illustrated as 23 (FIG. 3) and operated by a handle 22. Upon the slide 18 there is rotatably mounted a first plate 24 which sets in an annular roller bearing raceway 26 which is concentric about the vertically disposed axis of a pivot post 28. The pivot post 28 is arranged with a headed part 38 functioning to hold the plate 24 securely in the raceway 26 while permitting said plate 24 to rotate freely about the axis of the pivot post 28. In order to induce rotation of the plate 24, which, as it will become apparent hereinafter is essential to the generation of the toric surface 12, a cable 30 is attached at one of its ends 32 to one side of the arcuately shaped rear edge 34 of the plate 30 and is wrapped partially therearound so as to extend tangentially from said edge 34 toward the side 36 of the slide '18 and over a roller or pulley 3-8 which is supported by brackets 39 to the slide 18. The opposite end of the cable 36 is attached to a Weight 40 which is raised by a clockwise rotation of the plate 214 as viewed in FIG. 1 and upon release of the plate '24, the weight 40' functions to produce a pull on the cable 30 which causes rotation of the plate 24 in a counterclockwise direction as viewed in FIG. 3. A locking member 24a threaded through the plate 24 (see FIGS. 3 and 4) is provided to hold the plate 24 in a desired fixed oriented relation with the slide 18. By rotation of the handle 24b in the proper direction the threaded portion 240 of the member 24a will seat against the upper surface of the slide 18' and thereby lock the plate 24 against rotation relative to the slide 18. It will become apparent hereinafter that by means of the locking member 24a, the tool 56 can be held away from the position where the lens blank I0 is placed upon the head part 66 of the apparatus thereby permitting removal and replacement of the lens blank without interference from the action of the weight 46 tending to cause rotation of the plate 24. It should be understood that with the locking member released, rotation of the plate 24 can be produced either manually or automatically by means other than the weight 40. For example, a positive drive using a motor driven lead screw might be used or such a lead screw having a friction clutch between it and its drive motor would be suitable.

A second plate 41 carried by the first plate 24 is mounted in a guideway 43 (see FIG. 4) so as to he slidable longitudinally along the first plate 24 and locking means 45 is provided to secure the second plate 41 in a desired adjusted position upon the first plate 24.

A third plate which will be referred to hereinafter as the pivot plate 42 is mounted upon the second plate 41 and fastened thereto adjacent its forward end by means of a pivot stud 44 in such manner as to be pivotable about the axis of the stud 4 4. Locking means 46 is provided upon the pivot plate 42 by means of which said plate 42 may be secured against pivoting to the plate 24 when adjusted to a desired position thereon.

Upon the pivot plate 42 there is provided a slideway 48 in which a slide 50 carrying a motor mount 53 and motor 52 is slidable and can be locked to the guideway 48 with a set screw or cam lock arrangement indicated by the reference numeral 54. A dovetailed slide 72 is also pro-vided in the motor mount 53 to permit adjustment of said motor mount 53 in a direction normal to the direction of the 'guideway 48.

The cupped-type grinding tool 56 is mounted upon an adaptor 57 which, in turn, is fastened to the shaft of the motor 52 and openation of the motor 52 causes the tool 56 to rotate about its axis.

In the particular case illustrated in FIGS. 3 and 4, the tool 56 is designed to be used for generating negative toric surfaces such as illustrated in FIG. 1 and, for this. reason, it is provided With a convexly curved spherically shaped abrading face portion 58 which is preformed precisely to the radius of cylinder curvature desired upon the lens blank 10 (FIGS. 1, 3 and 4). That is, the radius of Ali) spherical curvature of the face portion 58 is equal to the radius of curvature to be formed along the meridian C of a lens blank such as shown in FIG. 1 as will be explained in more detail hereinafter with particular relation to the diagrammatic illustration shown in FIG. 6.

With further reference to the apparatus of FIGS. 3 and and 4, it will be seen that the work piece, which in this case will be considered to he the lens blank 10, is mounted in conventional fashion upon ia block 60 which is keyed by means of a pin and slot 62 to an adaptor 64 formed as a portion of the head part 66 of the apparatus. The head part is bolted or otherwise immovably fixed to the base 14 and, thus, the work piece or lens blank 10 when mounted upon the adaptor in the manner illustrated is fixed and immovable.

Considering FIG. 6 along with FIGS. 3 and 4, it will be seen that the setting up of the apparatus in FIGS. 3 and 4 and the operation of generating a negative toric surface 12 upon the lens blank 10' is accomplished as follows:

Knowing the radius of cylinder curvature desired upon the lens blank 16, a tool 56 having a true spherically curved abrading face part 5 8 precisely formed to said radius of curvature as indicated by the arrow 70 (FIG. 6) is selected and mounted upon the adaptor 57. The motor mount 53 carrying the motor and tool 56 is then adjusted laterally on the slide '50 by means of the dovetailed slideway '72 (see FIG. 4) to position a point 74 (see FIGS. 5 and 6) on the abrading face 58 of the tool in the vertical plane of a line 76 (see FIG. 6) extending through both the pivotal axis 78 of the stud 44 and the pivotal axis 89 of the pivot post 28 (see FIGS. 4 and 6).

The point 74 on the abrading face 58 of the tool 56 is preferably selected to be located adjacent the inner peripheral edge of the said abrading face 58 along an imaginary vertical line 82 (shown as a dash line in FIG. 5). This line 82 indicates approximately the position or line of contact on the abrading face of the tool where the full diameter of a lens blank It} having a diameter d (see FIG. 5) will be in complete contact with said tool during the grinding operation.

Having adjusted the tool laterally as just mentioned, it is then adjusted forwardly or rearwardly, as required, by moving the slide 56 to a position where the vertical axis 73 of the pivot stud 44 passes through the point 74 on the face of the tool 56. With the

slides

72 and 50 now locked to the above-mentioned adjusted positions, the pivot plate 42 is swung to such a position as to dispose the axis 84 of the tool (see FIG. 6) at an angle whose sine is equal to the distance K (see FIGS. 5 and 6), divided by the radius of curvature If? of the tool face 53. The distance K is the distance from the tool axis to the point 74 on the abrading face of the tool taken along a line perpendicular to the tool axis 84. The angle as which, as it can be seen, is actually a function of the diametrical size of the tool '56 and the curvature of its face portion can, and usually is, calculated and charted for each different tool size used and in this way by referring to a prepared chart, said angular setting is made on the apparatus of FIGS. 3 and 4 through the use of a suitably calibrated scale 86 on the plate 41 and a pointer 238 on the pivot plate 42.

As mentioned above, the cylinder curve or curvature along the meridian C of the lens blank 16 is formed automatically to a true shape during grinding as a result of the abrading face of the tool 56 being preformed to a true spherical curvature of a radius equal to that desired along the meridian C and the base curvature B of the lens blank is generated by swinging the tool 56 transversely across the lens blank along an arcuate path having a radius equal to that desired of said base curve B.

Knowing the radius of curvature desired for the base curvature B of the lens blank 10, the apparatus of FIGS. 3 and 4 is set to generate the same by adjusting the pivotal axis 84 of the pivot post 28 at a distance from the pivotal axis 73 of the pivot stud 44 equal to the said radius of base curvature. This is, in effect, placing the pivotal axis 80 from the point 74 on the tool face 58 at a distance equal to the base curve radius which is illustrated in FIG. 6 by the arrow 90. In the apparatus of FIGS. 3 and 4, this adjustment is made by moving the plate 41 along its guideway 43 on the rotatable plate 24 and thereafter locking the plate 41 to the plate 24 when the proper adjustment has been made.

It can now be seen that by pivoting the plate 24 about its pivot post 28 either manually or through the use of the cable 38 and weight 40 arrangement discussed above, the effective abrading face of the tool 56 will sweep across an arcuate path indicated as 92 in FIG. 6 which is equal in radius of curvature to that desired along the meridian B of the lens blank 10 in FIG. 1. It has been found that with the tool 56 rotating at a speed of approximately 3600 revolutions per minute and swung across the lens blank face at a rate of approximately .004 millimeters per each revolution of the tool while taking a cut of approximately .2 millimeters in depth a very desirable surface texture will be formed upon the lens blank surface. It is to be understood, however, that other similarly related speeds may be employed.

In order to bring the tool 56 and lens blank it into abrading relation with each other, the entire assembly of apparatus mounted upon the slide 18 is moved toward the lens blank 10 along the guideway 16. The slide 13 is locked to the guideway 16 when the relative positions of the tool 56 and lens blank 10 are such as to effect a desired depth of cut when the tool 56 is swept across the lens blank by being pivoted about the axis 80 of the pivot post 28.

It is pointed out that while the apparatus illustrated shows the lens blank 10 and its associated holding means as being immovable, it should be obvious that means might be provided to adjust the head part 66 in a direction toward or away from the tool '56 if desired. In any event, the depth of cut produced upon the lens blank 10 is established by moving the lens blank 10 and the tool 56, one toward the other, by any technique deemed suitable.

Referring in more detail to a step-by-step procedure which would normally be followed in the operation of generating toric surface 12 upon the lens blank 10 after once having set the apparatus of FIGS. 3 and 4 as just described, the plate 24 is initially rotated clockwise as viewed in FIG. 3 an amount sufiicient to position the tool away from the location of the lens blank 10 as shown diagrammatically in FIG. 6. The plate 24 is then locked to the slide 18 with the locking means 24a to hold this position. In so doing, an operator is free to position the blocked lens blank 10 upon the adaptor 64 without interference from the tool or from the force of the weight 40 tending to rotate the plate 24 in a counterclockwise direction.

With the lens blank 10 mounted upon the adaptor 64, as shown in FIGS. 3, 4 and 6, the plate 24 is unlocked from the slide 18 and the tool 56 is eased against the adjacent edge of the lens blank 10 by manually restraining the force of the weight tending to rotate the plate 24 counterclockwise. When the tool engages the lens blank, the natural force of the weight 40 is allowed to take over and continue the counterclockwise rotation of the plate 24 which carries the tool arcuately along the path 92 transversely across the lens blank 10 and produces the cut which generates the toric surface 12. The tool, 56, is at all times being rotated axially by the motor 52 as pointed out hereinabove.

Once having swept entirely across the lens blank 10 so that the tool is again out of engagement with the lens blank 10, the cut has been finished and the tool 56 is now located at the opposite side of the lens blank. At this time, the counterclockwise rotation of the plate 24 is stopped either automatically by having the bottom end of the weight strike a stop 40' or by again tightening the locking member 24a. Normally, at this time, the lens blank, along with its block 60, is removed for polishing. However, if it is desired to improve the surface texture of the lens blank resulting from the single cut or pass oil the tool over its surface, a second pass of the tool may be made over its surface 12 in a reverse direction (clockwise as viewed in FIG. 3). This is done by rotating the plate 24 back to its above-described starting point. Such a reverse pass is known to the trade as a sparking out operation which smoothens any minute surface irregularities which might occur or result from a single cut operation. The reverse cut would be accomplished with the apparatus illustrated herein by manual- 1y rotating the plate 24 clockwise against the pulling force of weight 44). However, as pointed out previously, refinements of the apparatus might embody automatically operated drives for rotating the plate 24 in either direction.

In all cases, with the apparatus shown herein, the initial cut on the lens blank 10 is made from right to left as viewed head on. Nevertheless, it should be understood that with other arrangements of the parts of the apparatus the initial cut could be made from left to right if desired. The procedure of generating and particular arrangement of the parts of the apparatus have been given only to illustrate the principles of the invention and are purely diagrammatic.

It can be seen that by following the above procedure, the radius of curvature along the meridian C of the lens blank 10 will be formed to a curvature which is of true cylindrical radius from edge-to-edge of the lens blank as a result of the tool having a true spherically curved abrading face part 58 and the radius of curvature along the meridian B will also be formed to a true radius from edge-to-edge of the blank as a result of the swing of the tool about the axis 18. Therefore, the surface 12 of the lens blank 10 is formed to a true toric curvature which is absolutely free of the commonly encountered elliptical errors or other errors of curvature.

It is pointed out that, in forming lens blanks such as 10 having differently curved negative toric surfaces, it is only necessary to provide and select a tool such as 56 having an abrading face portion accurately preformed to the specific curvature desired along the cylinder meridian C of the lens blank. The base curve along the base meridian B of lens blanks such as 10 may be changed simply by adjustment of the pivotal axis of the apparatus relative to the face of the tool. In setting the apparatus of FIGS. 3 and 4 for the generation of lens blanks to be provided with different negative toric surfaces the procedure outlined above is followed for each change of tool. 7

Referring now to the grinding action which takes place during the generation of a lens blank, emphasis is placed upon the fact that, in addition to producing true toric surfaces, an action producing a break-up motion between the tool face and the lens blank surface results during grinding. This break-up motion comes about from the use of the cupped-type tool which because of its being angled relative to the lens blank at all times during grinding and further being swept across the lens blank about an axis disposed normal to its axis of rotation, a combined rubbing and wiping grinding action takes place along progressively changing paths over the surface of the lens blank which produces a substantially uniform or homogenous surface texture upon the resultant lens blank surface. Such ground surfaces, being free of the heretofore commonly encountered elongated ridges or grooves resulting from milling with barrel-type tools or the like are adaptable to immediate polishing by optical standards. This is because the resultant texture of the surface is so fine and accurate that it needs no intermediate curve truing or fining operations and is a unique economical advantage gained by the practice of this invention. It is also pointed out that this break-up motion tends to eliminate wear differentials upon the tool surface and, in effect, produces a shape retaining feature actually functioning to remove tool surface irregularities such as slightly protruding diamond particles or the like thereby actually providing a tool surface shape-correcting feature. It is also pointed out that tools of the character described herein have reclaimability in that after prolonged periods of use where wear might result, the tools can be readily dressed or trued to remove slight errors of curvature.

Following the grinding of lens blanks such as 10, optical polishing of their abraded surfaces may be accomplished by any of the techniques well known to the trade. By way of illustration, polishing apparatus has been shown diagrammatically in FIG. 8 wherein the lens blank if still attached to its block 60 is placed face down upon a preformed polishing lap 94 having a toric surface configuration contrageneric to that having been generated upon the lens blank. Through the use of axis aligning means the lens is held with its base and cylinder meridians parallel to the same meridians of the lap surface and a polishing medium usually in liquid form is applied to the lap between its polishing surface and the lens blank while the lens blank is moved back and forth and circularly over said lap surface in restricted paths as is conventional.

Referring more particularly now to the forming of positive toric surfaces upon lens blanks such as shown in FIG. 2, it is pointed out the procedure followed is substantially identical to that described above with relation to the forming of negative torics. The major difference, however, is illustrated in FIG. 6 and lies in the fact that in forming positive torics, the tool and work holders are reversed upon the apparatus of FIGS. 3 and 4 so that the tool and its drive motor are mounted fixedly upon the head part 66 and the lens blank 10' is mounted to be stationary upon the part of the apparatus which was hereinabove described as being the motor mount 53.

The tool, in this case, which is referred to by numeral 199 in FIG. 7 is provided with an effective grinding face portion N2 which is concave and spherically shaped precisely to the base radius of curvature desired along the base meridian B of the lens blank it) (see FIGS. 1 and 6). This radius is indicated in FIG. 6 by the arrow 104.

In setting up the apparatus of FIGS. 3 and 4 for generating the positive toric lens blank 1'0 of FIGS. 2 and 7, the head 65 which is fixed upon the base 14 is set so as to orient the axis 1% of the tool 1% in such manner as to position the tool axis 106 at an angle relative to a line 110 extending through both the

pivotal axes

78 and 80 whose sine is equal to the distance K divided by the length of the base radius 104 (see FIG. 7). The distance K is measured perpendicularly from the axis 106 of the tool to a point 108 on the face 192 of the tool Also, by adjustment of the apparatus of FIGS. 3 and 4 using the slideway 72, the line 119 is positioned to have its vertical plane pass through the point 108. This procedure is analogous to the setting up of the angle qb and point 74 with line 76 in the case of generating negative torics as was described above and illustrated in FIG. 6.

With the apparatus adjusted to this point for generating positive torics, the relative positions of the axes 78 and 88 (FIG. 4) are adjusted by sliding the plate 41 relative to the plate 24 to set them at a distance apart equal to the radius of cylinder curvature desired along the meridian C (see FIG. 2) of the lens blank 10'. The tool 109 and lens blank 10 are then brought into grinding relation with each other and with the tool 100 rotating, generation of the positive toric surface 12 is accomplished by swinging the lens blank ill (now supported by the member 53) about the axis 80 which is illustrated in FIG. 7 as being the point 8%.

By so swinging the lens blank 10', its surface to be abraded passes along the arcuate path illustrated as 112 in FIG. 7 to produce the cylinder radius of curvature lb 114 along the meridian C (FIG. 2) of the lens blank 10. The base radius of curvature B (FIG. 2) is automatically formed in the direction of the meridian B as a result of the tool face 102 being preformed to a true spherical shape of a radius of curvature 104 equal to that desired for the base curve of lens blank 10'.

It can now be seen that, to generate differently curved positive toric surfaces on lens blanks, it is only necessary to provide a tool having the desired base curvature, that is, one for each different base curve. Changes in cylinder curvature are accomplished by adjustment of the apparatus.

In all cases of either negative or positive toric generation described above true toric surfaces will be formed as a result of the tool faces being preformed to true spherical curvatures of radial dimensions selected to be precisely equal to the curvature desired along at least one of the major meridians of each of the lens blanks and by swinging the tool relative to the blanks in a controlled radial arc.

Also, in the case of positive toric generation, the abovedescribed break-up motion will be present during grinding and will produce an all over substantially uniform surface texture such as to permit direct optical polishing of the resultant ground lens blank. In the polishing of positive toric surfaces with apparatus such as shown in FIG. 8, the illustrated tool and lap would normally be reversed in position and the lap being placed over the lens blank would have a concave toric surface precisely formed contrageneric to the curvature of the convex toric surface of the lens blank.

From the foregoing, it can be seen that improved, simplified and economical means and method have been provided for accomplishing all of the objects and advantages of the invention. However, it should be apparent that many changes in the details of construction, arrangement of parts and steps in the process may be made by those skilled in the art without departing from the spirit of the invention as expressed in the accompanying claims and the invention is not to be limited to the exact matters shown and described as only the preferred matters have been given by way of illustration.

Having described my invention, I claim:

1. The method of generating a curved surface upon an article such as a lens blank comprising supporting said article in such a position as to be engaged by an annular abrading face part of an axially rotating grinding tool whose face part is of appreciable width and is provided with a true spherical shape throughout saidwidth which is of a radius of curvature equal to that desired along one meridian of the surface being formed on said article, swinging said tool and article, one transversely relative to the other, about an axis disposed normal to the axis of rotation of said tool and spaced from the portion of the inner edge of said annular abrading face part which is located on the side of the axis of rotation of the tool nearest the article and at a selected distance equal to a different radius of curvature desired upon the surface of said article in the direction of another major meridian thereof, said spherically curved annular abrading face part of appreciable width and said inner edge portion thereof, during said swinging movement of the tool and article relative to each other causing a combined rubbing and wiping abrading action along progressive different paths over the surface being generated whereby the spherical curvature of said face part controls and produces the true curvature desired in said one meridian of the surface being generated and said inner edge of said annular abrading face part and the path of movement thereof controls and produces the true different curvature desired in said other major meridian of the surface being generated and results in an overall surface texture suitable for direct subsequent polishing.

2. The method of generating a ground toric surface upon an article such as a lens blank comprising supporting said article in such a position as to be engaged by an annular abrading face part of an axially rotating grinding tool whose face part is of appreciable width and is provided a with a true spherical shape throughout said width which is of a radius of curvature equal to that desired along a first major meridian of the surface being formed on said article, swinging said tool and article, one transversely relative to the other, about an axis disposed normal to the axis of rotation of said tool and spaced from the portion of the inner edge of said annular abrading face part which is located on the side of the axis of rotation of the tool nearest the article and at a selected distance greater than that of the radius of spherical curvature of said face portion of said tool and controlled to be equal to the radius of curvature desired upon the surface of said article in the direction of a second major meridian thereof which is disposed at right angles to said first major meridian, said spherically curved annular abrading face part of appreciable width and said inner edge portion thereof, during said swinging movement of the tool and article relative to each other causing a combined rubbing and wiping grinding action along progressive different paths over the surface being generated whereby the spherical curvature of said face part con trols and produces the true curvature desired in said first major meridian of the surface being generated and said inner edge of said annular abrading face part and the path of movement thereof controls and produces the true different curvature desired in said second major meridian of the surface being generated and results in an overall surface texture suitable for direct subsequent polishing.

3. The method of generating a negative toric surface upon an article such as a lens blank comprising supporting said article in such a position as to be engaged by an annular abrading face part of an axially rotating cuppedtype grinding tool whose face part is of appreciable width and is provided with a true convex spherical shape throughout said width having a radius of curvature equal to that being formed along a first major meridian of the surface of said article, feeding said tool in an arcuate path transversely across said surface of the article about an axis disposed normal to the axis of rotation of said tool and spaced rearwardly from the portion of the inner edge of said annular abrading face part which is located on the side of the axis of rotation of the tool nearest the article and at a radial distance greater than the radius of curvature of said spherical face portion of said tool and controlled to be equal to the radius of curvature desired upon the surface of said article in the direction of a second major meridian of said surface and which is at right angles to said first major meridian, said spherically curved annular abrading face part of appreciable width and said inner edge portion thereof, during the feeding of the tool in an arcuate path transversely across the surface of the article, causing a combined rubbing and wiping abrading action along progressive different paths over said surface being generated whereby the spherical curvature of said face part controls and produces the true curvature desired in said first major meridian of the surface being generated and said inner edge of said annular abrading face part and the arcuate path of movement thereof controls and produces the true dilferent curvature desired in said second major meridian of the surface being generated and results in an overall surface texture suitable for direct subsequent polishing.

4. The method of generating a positive toric surface upon an article such as a lens blank comprising supporting said article in such a position as to be engaged by an annular abrading face part of an axially rotating cupped-type grinding tool whose face part is of appreciable width and is provided With a true concave spherical surface shape throughout said width having a radius of curvature equal to that being formed along a first major meridian of a surface of said article, feeding said article in an arcuate path transversely across said spherically shaped annular abrading face part of said tool about an axis disposed normal to the axis of rotation of said tool and spaced forwardly from the portion of the inner edge of said spherically shaped annular abrading face part which is located on the side of the axis of rotation of the tool nearest the article and at a radial distance less than the radius of spherical curvature of said annular face part of said tool and controlled to be equal to the radius of curvature desired upon said surface of said article in the direction of another major meridian, said spherically curved annular abrading face part of appreciable width and said inner edge portion thereof, during the feeding of said article in an arcuate path transversely across said spherically-shaped annular abrading face part, causing a combined rubbing and wiping abrading action along progressive different paths over the surface being generated whereby the spherical curvature of said face part controls and produces the true curvature desired in said first major meridian of the surface being generated and said inner edge of said annular abrading face part and the path of movement thereof controls and produces the true different curvature desired in said second major meridian of the surface being generated and results in an overall surface texture suitable for direct subsequent polishing.

5. Apparatus for forming a ground curved surface upon a work piece such as a lens blank comprising work holding means, a rotatable grinding tool having an annular abrading face part of appreciable width and which is preformed to a true spherical shape throughout said Width of a radius of curvature equal to that desired upon a surface of said work piece along a first meridian thereof, said annular abrading face part further having an inner edge portion adapted to produce a different curve in a second meridian normal to said first meridian, means for rotating said tool about its axis, means for supporting said work piece in said work holding means, means for moving said rotatable tool and work holding means one toward the other to bring said surface of said work piece and said annular abrading face part of said tool into engaging relation with each other, means for swinging said tool and work piece, one transversely relative to the other, about an axis disposed normal to the axis of said tool and spaced from the portion of the inner edge of said annular abrading face part of said tool which is located on the side of the axis of rotation of the tool nearest the work piece and at a distance equal to the radius of curvature desired upon said surface of said work piece in the direction of said second meridian thereof normal to said first meridian, said annular abrading face part of appreciable width and said inner edge portion thereof, during said swinging movement of the tool and work piece relative to each other, being adapted to cause a combined rubbing and Wiping abrading action along progressive different paths over the surface being generated whereby the spherical curvature of said surface part controls and produces the true curvature desired in said first meridian of the surface being generated and said inner edge of said annular abrading face part and the path of movement thereof controls and produces the true different curvature desired in said second meridian of the surface being generated and results in an overall surface texture suitable for direct subsequent polishing.

6. Apparatus for forming a ground compound curvature upon a surface of a work piece such as a lens blank comprising work holding means, a rotatable cupped-type grinding tool having an annular abrading face part of appreciable width and which is preformed to a true spherical shape throughout said width of a radius of curvature equal to that desired upon said surface of said work piece along a first major meridian thereof, said annular abrading face part having an inner edge portion adapted to produce a different curve in a second meridian normal to said first meridian, means for rotating said tool about its axis, means for supporting said work piece in said work holding means, means for adjusting said work hold- 113 ing means and said rotatable tool, one toward the other, to such related positions as to engage said surface of said Work piece with said annular abrading face part of said tool, means for swinging said tool and Work piece, one transversely relative to the other, along an arcuate path about an axis disposed normal to the axis of said tool and spaced from the portion of the inner edge of said annular spherically shaped abrading face part of said tool which is located on the side of the axis of rotation of the tool nearest the work piece and at a distance dimensionally different than said radius of spherical curvature or" said annular face part of said tool and said distance being selected to be equal to said radius of curvature desired upon the surface of said Work piece in the direction of said second major meridian thereof normal to said first major meridian, said annular abrading face part of appreciable width and said inner edge portion thereof, during said swinging movement of the tool and work piece relative to each other, being adapted to cause a combined l4 rubbing and Wiping abrading action along progressive different paths over the surface being generated whereby the spherical curvature of said surface part controls and produces the true curvature desired in said first meridian of the surface being generated and said inner edge of said annular abrading face part and path of movement thereof controls and produces the true different curvature desired in said second meridian of the surface being generated and results in an overall surface texture suitable for direct subsequent polishing.

References Cited in the file of this patent UNITED STATES PATENTS 2,351,095 Blanchon June 13, 1944 2,545,447 Clement Mar. 20, 1951 2,633,675 Ellis Apr. 7, 1953 2,916,857 Dargie Dec. 15, 1959 3,021,647 Cretin Maitenez Feb. 20, 1962 3,032,936 Voice May 8, 1962

Claims

5. APPARATUS FOR FORMING A GROUND CURVED SURFACE UPON A WORK PIECE SUCH AS LENS BLANK COMPRISING WORK HOLDING MEANS, A ROTATABLE GRINDING TOOL HAVING AN ANNULAR ABRADING FACE PART OF APPRECIABLE WIDTH AND WHICH IS PERFORMED TO A TRUE SPHERICAL SHAPE THROUGHOUT SAID WIDTH OF A RADIUS OF CURVATURE EQUAL TO THAT DESIRED UPON A SURFACE OF SAID WORK PIECE ALONG A FIRST MERIDIAN THEREOF, SAID ANNULAR ABRADING FACE PART FURTHER HAVING AN INNER EDGE PORTION ADAPTED TO PRODUCE A DIFFERENT CURVE IN A SECOND MERIDIAN NORMAL TO SAID FIRST MERIDIAN, MEANS FOR ROTATING SAID TOOL ABOUT ITS AXIS, MEANS FOR SUPPORTING SAID WORK PIECE IN SAID WORK HOLDING MEANS, MEANS FOR MOVING SAID ROTATABLE TOOL AND WORK HOLDING MEANS ONE TOWARD THE OTHER TO BRING SAID SURFACE OF SAID WORK PIECE AND SAID ANNULAR ABRADING FACE PART OF SAID TOOL INTO ENGAGING RELATION WITH EACH OTHER, MEANS FOR SWINGING SAID TOOL AND WORK PIECE, ONE TRANSVERSELY RELATIVE TO THE OTHER, ABOUT AN AXIS DISPOSED NORMAL TO THE AXIS OF SAID TOOL AND SPACED FROM THE PORTION OF THE INNER EDGE OF SAID ANNULAR ABRADING FACE PART OF SAID TOOL WHICH IS LOCATED ON THE SIDE OF THE AXIS OF ROTATION OF THE TOOL NEAREST THE WORK PIECE AND AT A DISTANCE EQUAL TO THE RADIUS OF CURVATURE DESIRED UPON SAID SURFACE OF SAID