Method Of Producing Variable Profile Bi-focal Lens

Abstract

Bi-focal blanks are produced which have constant optical centering for minimization of vertical imbalance, the blanks produced by pre-selecting one or more diopter series having predetermined distance, then establishing a pair of terminal lines from a central point equal to the diopter distance to finite positions above and below said dividing line representing the optical centering of the line, then developing a plurality of radii from each of said terminal lines to each of the distance and reading portions, then placing the lens blank on a lens-blocking wheel and grinding with a first tool to a first curvature, then deblocking and blocking on a smaller wheel and grinding with another cut tool to form the other curvature, both these curvatures being the distance and reading powers required for minimization of vertical imbalance.

Description

BACKGROUND AND OBJECTIVES

Present day bi-focal spectacles are generally selected from stock blanks and ground down to conform to prescription requirements. The blanks traditionally have been made with the distance-near optical center proximity at a fixed relationship angularly.

When there is a balance-equal vision in both eyes the use of bi-focals does not create any real physical problem in going from the distance level to reading level with the exception of image displacement. However, when there is an imbalance in vision between both eyes, one eye views the distance and reading from different optical centers than the other. This imbalance is generally referred to as vertical imbalance. Prism is measured by the number of millimeters the eye wanders away from the optical center multiplied by the power of the lens in a given meridian. The difference in prismatic effect between the two lenses is the vertical imbalance. This problem essentially occurs when the correction for each eye is of a different dioptric power than the other. The degree to which the vertical imbalance becomes a problem depends on the magnitude of the difference in dioptric correction for each eye.

Vertical imbalance has always been corrected by what is known as "slab-off;" that is, the blanks are specially ground by skilled technicians to assure proper balance. However, the use of skilled technicians is expensive, time-consuming and dependant upon the skill of the operator and at best only balances prisms and does not provide the viewer with the advantage of viewing through the optical centers of the lenses. The elimination of vertical imbalance in bi-focals must be automatic to the point where the selection of the proper blanks may be done by unskilled or semi-skilled personnel. In other words, there should be a built-in system where the semi-finished blanks are structured in categories so designed as to cover every conceivable vertical imbalance situation so that mere pre-selection of the blank would automatically take into consideration vertical imbalance.

Bi-focal blanks traditionally have been made with the distance-near proximity as a fixed relationship angularly to produce a constant optical centering.

It is the purpose of this application to provide for built-in variations of the distance-near angular relationship, on the convex side of the blank that automatically balances distance and near optical centers.

It is another object of the invention to provide a system for producing bi-focal lenses that eliminates or reduces vertical imbalance to a minimum.

Another object of the invention is to provide a system for producing bi-focal lenses that is simple, economical and efficient.

A still further object of the invention is to provide a system for producing bi-focal blanks having pre-selected distance-near relationships that provide systematic compensation for vertical imbalance and image displacement.

A still further object of the invention is to provide a system for producing a multiple series of multi-focal blanks and wherein grinding tool selection closely adheres to prescription requirements.

Another object of the invention is to provide a system for producing lens blanks that vary in angular relationship "distance portion" to "reading portion" so as to produce a constant optical centering in that the distance optical center and the reading optical center would always locate at the most desirable pre-determined setting in the completed bi-focal lens regardless of prescriptive requirements.

Further objects and advantages will become apparent from a reading of the specifications and a study of the accompanying drawings, and wherein;

FIG. 1 shows a simplified drawing of bi-focal spectacles with the placement of distance-near optical proximity centers;

FIG. 2 illustrates the presentation of a present-day bi-focal blank with centers of the distance-near radii on the same line dividing two fields.

FIG. 3 is similar to FIG. 2 except the two semi-circular segments are rotated away from each other.

FIG. 4 is similar to FIG. 2 except that the two semi-circular segments are rotated towards and inward to each other.

FIGS. 5a, b, c, d, and e represent schematically the angular deviation of both distance and reading theoretical lines from the present-day line from which the respective radii are drawn.

FIGS. 6a, and 6b illustrate a method of grinding present-day bi-focal lenses, and is a part of the prior art.

FIGS. 7, 8 and 8a show the lens blocking wheel and grinding tools for grinding the distance and reading portions of the bi-focal blanks.

FIG. 9 illustrates the bi-focal blank with centers of the distance-near radii on different dividing the two fields according to one embodiment of the invention.

FIG. 10 illustrates the bi-focal of FIG. 9 according to still another embodiment of the invention.

Now describing the invention in more detail according to the different embodiments, there is shown in FIG. 1 a pair of bi-focal spectacles 1 having a pair of lens 2 and 3, each of said lens being split into an additional pair 4, 5 and 6, 1, respectively. In general, the upper lens 4 and 6 are for distance vision, each having optical centers 7 and 8 and the lower lens 5 and 1 are for near vision, each having optical centers 9 and 10. The four optical centers as shown represent a structure wherein the user would not experience vertical imbalance nor image displacement.

The construction of a pair of bi-focal spectacles generally starts from the selection of the proper semi-finished blanks 11, shown in FIG. 2, which in effect is composed of two semi-finished lens surfaces 12, 13, with two different radii of curvature made from a single glass blank having a single radius of curvature 15 on the concave portion of the blank that is unfinished and different radii of curvature 16 and 17 on the outer convex portion of the said blank is a continuation of surfaces 12, 13. The outer radii 16, 17 represent the optical parameters or powers for meeting the required prescriptive measurements. The center of curvature 18 from which the radius 16 is taken, representing the curvature 18 from which the radius 16 is taken, representing the curvature for the inner part of the blank is placed on a base line 19 which represents the separation of fields 20, 21 from which the radii 16 and 17 have their center. This base line 19 may also be referred to as the theoretical line. Thus, there is produced what is called a mono-centric bi-focal. However, the two centers being exactly on the same base or theoretical line serves the user adversely since he cannot view through the distracting obstruction (the line separating the reading and distance portion) of the bi-focal lens. He must look above the line to see through the distance area, and below the line to see through the reading area. If it happens that the lenses for the right and left eyes are of equal power, the wearer will experience image displacement a consequent of looking away from the optical center of the lens. As previously discussed, this is not an ideal optical condition and is not the primary factor herein for the invention, but rather for the prevention of a much more serious eye discomfort called vertical imbalance in bi-focals. This problem occurs when the correction for each eye is of a different dioptric power. The degree to which the vertical imbalance becomes a problem depends on the magnitude of the difference in dioptric correction for each eye.

FIGS. 3 and 4 are comparable to FIG. 2 but as in FIG. 3 the two fields are pried apart by a finite angle A and in FIG. 4 they are forced together by a finite angle B. Both FIGS. 3 and 4 present exaggerated extremes of the profile. It is this variation in profiles by which semi-finished blanks will produce bi-centering that is standard within acceptable limits. This standard bi-centering could be accomplished by creating three different series of plus-base semi-finished bi-focal blanks of series -4, -6, and -8. Each of these curves would be keyed angularly to a semi-finished plus base curve and its reading made additive. These base series are merely illustrative and any series can be utilized. It is the angular relationship of each series between base and reading portions that is maintained in a fixed arrangement so as to produce a constant optical centering and thereby effect a reading-optical and distance optical center that is most desirable to the user.

The optical centers of distance and reading portions in bi-focals in general are believed by some authorities to be approximately 8 millimeters apart. Technicians in the ophthalmic industry generally know which base (distance) curve blank to use for a given prescription power. With the lens blanks described herein the technician would have to select the proper series after he selects the proper base for the prescription he is to grind. He would have to select a series number that is closest to the number of the grinding tool he will be using for his particular prescription. Because of the varying angular relationship of distance (base) to reading, the distance portion optical center would always locate approximately 3 millimeters above the dividing line (the line dividing the bifocals) and the reading portion optical center would always locate approximately 5 millimeters below the dividing line. These distances above and below the said dividing line can be set to any arbitrary figure as dictated by the need of the profession.

The angular relationships, exaggerated by FIGS. 3 and 4 may be more clearly defined and illustrated as shown by FIGS. 5a - e. FIG. 5a shows the theoretical line 25 of present-day bi-focals also set at an angle of 90.degree. from a reference line 26. It is this line 26 from which the distance portion radius 27 and the reading radius 28 are drawn. FIGS. 5b and 5c show the theoretical line varying from the original setting, in one case it is 88.degree. 21' and the other 91.degree. 32' for the base or distance portion of the bi-focal. In FIGS. 5d and 5e, the theoretical line for the reading portion varies from 88.degree. to 94.degree. 23'.

From FIGS. 5b and 5c when the theoretical line varies from the angle 88.degree. 21' to 91.degree. 32', it was empirically found that the distance portion optical center always was found to be 3 millimeters above the dividing line. For the reading portion, as shown by FIGS. 5d and 5e, it was also found empirically that where angle varies from 88.degree. to 94.degree. 23' the location of the reading optical center would be 5 millimeters below the dividing line.

Presently, bi-focals are produced by setting the distance portion (base) tool 30, shown in FIG. 6a exactly on center so that they are ground and polished prism free. The lens blanks 31 are first placed on a blocking wheel 32 and ground down to meet the distance portion of the blanks or bi-focals by use of the aforementioned grinding tool 30. After the required grinding has been effected, the lens blanks are de-blocked from the wheel 32 and placed on a smaller diameter wheel 33, as shown in FIG. 6b. Here, again, lens grinding is effected by a smaller radius grinding tool 34 that is cut exactly in half. This latter grinding is for producing the reading portion of the blank. The more sophisticated methods for grinding lenses using the wheel and grinding tool above mentioned may be gleaned from the art and also from U.S. Pat. No. 2,847,804, Calkins, et al. The production of blanks as contemplated by the instant invention, the grinding tool must be shifted varying amounts either to left or right to meet the requirements set by the angular variations of 88.degree. 21' to 91.degree. 32' shown in FIGS. 5b and 5c. FIG. 7 shows partially the blocking wheel 40 and lens blank 41 residing circumferentially thereon with grinding tool 42 positioned for proper cutting. The blank is ground and polished accordingly with the tool shifting to produce the controlled angular variations previously defined.

In producing the second half, the reading portion, the smaller radius tool again has to be cut, as shown in FIGS. 8 and 8a, but not exactly in half as in producing the present-day blanks. Instead, the tool will vary in being partially sectioned or cut just short of half to slightly more than half of full size. Only the reading portion tools are cut, whereas distance portion is produced by shifting full-size tools left or right. The shifting of tools, either full-size or cut, varies in different amounts and in different degrees depending to what extent the base and reading lines have shifted from the theoretical lines as previously mentioned.

FIGS. 9 and 10 show different blank series and how a lens is developed to maintain minimum vertical imbalance. In FIG. 9, as an example, a 4 diopter series (132.5 mm.) is chosen and two radii 53 and 51, called terminal lines, are drawn from a central point 52 to the inner lens blank surface 54, one (53) 3 mm. above the blank dividing line 55 and the other (51) 4 mm. below the blank dividing line. The lengths of the radii are 132.5 mm. or 4 diopters. These radii or terminal lines then become the loci for all centers of radii for the base and reading curves. FIG. 10 is comparable to FIG. 9, where the series represents a diopter of 8 (66.2 mm.). Here, again, the center of radii 60 and 61 originate at a point 62 and terminate 3 mm. above and 5 mm. below the bi-focal dividing line 63. However, it can be seen here that the distance and reading radii 64 and 65, respectively, are longer than the diopter radii 60, 61. Hence, these latter radii must be extended to 66 and 67 to assure that the radii 64 and 65 have lines to extend from.

In the foregoing manner uniform centering for the whole multiple series and multiple base curves are formed that eliminates or minimizes vertical imbalance and image displacement.

It can be appreciated that the foregoing represents particular embodiments of the invention and that there are various changes and modifications which can be made and further defined without detracting from the true scope and extent of the invention. For example, the development and cutting of the various blanks according to any given series may be extended not only to glass but also to the production of plastic blanks. For example, any series blank cut from glass according to the invention may then be used to produce molds for plastic bi-focals.

Claims

Having defined the invention, what is claimed is:

1. In a system for producing bi-focal lens of constant optical centering from semi-finished blanks having reading and distance portions separated by a dividing line, the method comprising,

a. the pre-selection of one or more diopter series having pre-determined distances,

b. establishing a pair of equal terminal lines from a central point equal to said diopter distance to finite positions above and below said dividing line representing the optical centering of the lens,

c. developing a plurality of radii from each of said terminal lines to each of the distance and reading portions, each of said radii being comparable to the prescriptive powers of the respective distance and reading portions of the lens,

d. placing each of a plurality of lens blanks of each series on a lens blocking wheel whose radius is comparable to the radius of curvature of the distance portion of said bi-focals in one direction,

e. grinding the lens on said wheel with a first shiftable grinding tool having a preselected radius of curvature to effect grinding of the lens according to selected distance optical powers, and capable of being shifted in a direction equal to the selected variation of said distance optic powers,

f. de-blocking lens blanks from said wheel and placing same on a second blocking wheel whose radius is comparable to the reading portion of said bi-focals in one direction, and

g. subjecting said wheel to the grinding action of a second partially sectioned grinding tool having a radius of curvature in another direction to said blocking wheel and disposed to being shifted in a direction equal to the variations of reading optic powers, the completed blanks of each selective series having constant optical centering for the minimization of vertical imbalance.

2. In a system according to claim 1 and wherein said diopter series is equivalent to plus-base series -4, -6 and -8.

3. In a system according to claim 1 and wherein said finite positions above and below said dividing line is 3 millimeters and 5 millimeters, respectively.

4. In a system according to claim 1 and wherein said second partially sectioned grinding tool is greater than one-half of the full size of said tool.

5. In a system according to claim 1 and wherein said second partially sectioned grinding tool is less than one-half of the full size of said tool.