Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2001-02-27
2002-07-16
Eley, Timothy V. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S042000
Reexamination Certificate
active
06419549
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a manufacturing method of right and left spectacle lenses and system thereof. Particularly, the present invention is effective when the right and left spectacle lenses have different focal powers to each other. The spectacle lenses may be single-vision lenses or progressive-power lenses.
Spectacles consist of right and left lenses and a frame that holds these lenses. When the powers required for the right and left lenses are equal to each other, shapes of the front surface (an object side) and the back surface (an eye side) of the right lens are the same as that of the left lens. On the other hand, when right and left lenses whose powers required are largely different are independently designed, the shape of the right lens is largely different from the shape of the left lens, which loses a balance between the shapes of the right and left lenses, exacerbating an outward appearance thereof. Since the outward appearance depends on the shapes of the front surfaces, the shapes of the front surfaces should be identical with each other to enhance the outward appearance.
A technique to equate shapes of front surfaces to keep the balance between right and left lenses has been known as prior art. For instance, Japanese patent provisional publication No. Hei 8-320457 discloses the technique to independently design shapes of right and left lenses according to a prescription at a first step, and to redesign at least one of the right and left lenses so that the curvatures of the front surfaces are approximate to each other.
However, the above described publication does not describe optical performances of right and left lenses after the redesigning. In general, since a lens form (i.e., a combination of shapes of front and back surfaces) to produce the given focal power is limited to minimize aberrations, when the lens is redesigned with only considering the shapes of the front surfaces, the aberrations becomes large, exacerbating the optical performance.
Namely, in the case of a spherical lens, a lens form to minimize aberrations is substantially uniquely determined with respect to the focal power when the lens material is predetermined. Therefore, when the focal powers required for right and left lenses are different to each other, the aberrations of at least one of the right and left lenses must increase as a result of redesigning to equate the shapes of the front surfaces.
On the other hand, in the case of an aspherical lens, a range of choices of shapes for a specific refractive power is broader than in a spherical lens. However, when the difference between the focal powers of the right and left lenses becomes large, it is inevitable that the aberration increases due to the redesigning. A conventional aspherical spectacle lens has an aspherical front surface and a spherical back surface. Semifinished lens blanks whose aspherical front surfaces are finished are stockpiled in a manufacturing factory. In a conventional manufacturing method, shapes of front surfaces of right and left lenses are determined among various predetermined shapes based on specifications of a customer in a first step. In a second step, curvatures of back surfaces of the right and left lenses are calculated on the basis of the specification and the determined shape of the front surfaces. In an actual processing step, a pair of semifinished lens blanks are selected among various stockpiled blanks and they are placed on a surface processing machine. Then, the back surfaces of the selected semifinished lens blanks are processed with the surface processing machine on the basis of the calculated curvatures. There are different types of semifinished lens blanks corresponding to various focal powers. That is, the entire range of a focal power required for a spectacle lens is divided into a plurality of sections and each aspherical surface is assigned to each section. Since processing of an aspherical surface was difficult with the conventional processing machine, it was important to limit the types of aspherical surfaces in order to reduce manufacturing cost.
Each aspherical surface is designed so as to keep an optical performance when the aspherical surface covers the focal power within the specific section. Therefore, when a lens having a predetermined focal power is manufactured using an aspherical surface that is assigned to a different section, the optical performance becomes worse significantly. Namely, when the aspherical front surfaces of right and left lenses whose focal powers are not within the same section are formed to be identical, an optical performance of either right lens or left lens that employs an aspherical surface of the different section becomes worse significantly.
Design examples of conventional single-vision spherical lenses and conventional single-vision aspherical lenses will be described.
FIGS. 39A and 39B
are sectional views of the conventional spherical lenses when the right and left lenses are independently designed. In the drawings described below, (R) represents the right lens and (L) represents the left lens. In each lens diagram, the surface at the left is a front surface and the surface at the right is a back surface. In this example, spherical powers (SPH) required for the right and left lenses are −4.00 diopter and +2.00 diopter, respectively. TABLE 1 shows numerical construction of each lens. In TABLE 1, R
1
denotes a radius of curvature of the front surface, R
2
denotes a radius of curvature of the back surface, T denotes a center thickness, N denotes a refractive index and &phgr; denotes a diameter of the semifinished lens blank. Units of R
1
, R
2
, T and &phgr; are millimeters (mm).
TABLE 1
(R)
(L)
SPH
−4.000
2.000
R1
150.000
85.714
R2
74.906
117.693
T
1.000
3.147
N
1.600
1.600
&phgr;
70.000
70.000
Base curves (surface power of front surface) of the right and left lenses are 4.00 diopter and 7.00 diopter, respectively.
FIGS. 40A and 40B
show astigmatisms of the right and left lenses. In each of graphs, a solid line represents the astigmatism A
∞
for distance vision (object distance: ∞) and a dotted line represents the astigmatism AS
300
for near vision (object distance: 300 mm). In the graphs of astigmatism, the horizontal axis denotes an amount of astigmatism (unit: diopter) and the vertical axis denotes a visual angle (unit: degree).
The respective spectacle lenses have satisfactory optical performances, while the outward appearance lacks in balance between the right and left lenses because of the difference between the base curves. Thus, the design of the left lens will be changed such that the base curve of the left lens matches to that of the right lens. Numerical constructions after the design change are shown in TABLE 2.
FIGS. 41A and 41B
show sectional views of the spectacle lenses after the design change.
FIGS. 42A and 42B
show astigmatisms AS
∞
for distance vision and the astigmatism AS
300
for near vision of the spectacle lenses after the design change.
TABLE 2
(R)
(L)
SPH
−4.000
2.000
R1
150.000
150.000
R2
74.906
295.421
T
1.000
3.060
N
1.600
1.600
&phgr;
70.000
70.000
Since the base curves of the right and left lenses become identical (4.00 diopter), the front surfaces have the common shape. As shown in
FIG. 42B
, however, the astigmatism of the left lens for distance vision becomes significantly large as compared with the condition before the design change.
Next an example of aspherical lenses will be described.
FIGS. 43A and 43B
are sectional views of the conventional aspherical lenses that are independently designed. The front surfaces are rotationally symmetrical aspherical surfaces and the back surfaces are spherical surfaces. In this example, SPH required for the right and left lenses are −4.00 diopter and −8.00 diopter, respectively. TABLE 3 shows numerical construction of each lens. R
1
represents a radius of curvature at the center.
TABLE 3
(R)
(L)
SPH
−4.000
−8.000
R1
300.000
1200.000
R2
99.958
70.587
T
1.000
1.000
Asahi Kogaku Kogyo Kabushiki Kaisha
Eley Timothy V.
Greenblum & Bernstein P.L.C.
Nguyen Dung Van
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