Games using tangible projectile – Golf – Ball
Reexamination Certificate
1999-12-20
2001-07-03
Graham, Mark S. (Department: 3711)
Games using tangible projectile
Golf
Ball
C473S383000
Reexamination Certificate
active
06254496
ABSTRACT:
This invention relates to a dimpled golf ball having improved aerodynamic isotropy and covering equal distance, and a method for distributing a plurality of dimples on a golf ball.
BACKGROUND OF THE INVENTION
Current golf balls have dimples in their surface. For the dimple distribution, regular octahedral, regular icosahedral and regular polyhedral arrangements are generally employed. A spherical surface is divided as a regular polyhedron to define surface units, typically triangular surface units, where dimples are arranged. These arrangements are effective in enabling easy dimple design and mold manufacture and achieving good aerodynamic isotropy.
These arrangements, however, have the following problem. In the respective surface units, dimples are arranged in the same pattern, that is, the same pattern is repeated. The patterns are regular so that the dimples and the lands between dimples (i.e., surface areas where no dimples are formed) are arranged in a regular manner. In one example, dimples and lands are arranged in a row. A golf ball having dimples repetitively arranged in the same pattern exhibit different aerodynamic properties depending on the axis of rotation which varies with a particular point of impact, leading to variations of distance. The dimple arrangement based on the above-described units encounters a limit in closely distributing dimples and is hardly regarded as exerting maximum aerodynamic performance.
More particularly, it was found that the dimple arrangement based on the above-described units has the problem that aerodynamic properties largely differ whether or not the boundary between the units is coincident with the direction of rotation. This is because the units are large. The difference of aerodynamic properties is very significant between hemispheres which are regarded as the maximum unit in the prior art arrangement method. The difference of aerodynamic properties between equatorial rotation and longitudinal rotation is large enough to be perceivable in an actual hitting test and demonstrated by the measurement results of a swing machine test.
A number of approaches have been proposed for eliminating such a difference of aerodynamic properties, but none of them have given a sweeping solution. Since all these approaches are halfway measures to correct the difference while maintaining the arrangement units unchanged, they fail to significantly improve aerodynamic isotropy.
SUMMARY OF THE INVENTION
An object of the invention is to provide a golf ball having improved aerodynamic isotropy and covering equal distance. Another object of the invention is to provide a method for distributing a plurality of dimples on a golf ball so as to give a full solution to the aerodynamic anisotropy.
In a first aspect, the invention provides a golf ball having a plurality of dimples in its surface. The dimples as a whole are randomly distributed on at least a hemispherical surface. In preferred embodiments, the dimples are circular or non-circular or both in plane shape, the dimples are different in diameter or depth or both, and the dimples each have an area of 3 to 30 mm
2
when projected on a plane.
In a second aspect, the invention provides a method for arranging a plurality of dimples on a golf ball, comprising the steps of initially distributing the plurality of dimples on a surface of a computer golf ball model, selecting one dimple and performing on the one dimple at least one alteration selected from movement and rotation of the one dimple and geometrical enlargement or contraction of dimples such that the sum of the squares of boundary spherical distances between the one dimple and adjacent dimples may be minimum and the dimples may not overlap each other, and iterating the alteration on the remaining dimples.
The alteration operation is terminated when the value of Sk is smaller than a desired convergence criterion value, said Sk being given by the equation:
Sk
=
∑
i
=
1
N
∑
j
=
1
Mi
Lij
2
wherein i, j and k are counters, Sk is the sum of the squares of distances between adjacent dimples, calculated for all the dimples, 1 is added to k whenever optimization is performed on all the dimples, N is the total number of dimples, Mi is the number of dimples adjoining an i-th dimple, and Lij is the distance between an i-th dimple and a i-th dimple among a Mi number of dimples adjoining the i-th dimple. The dimple distribution thus obtained provides a dimple arrangement on the golf ball.
In the golf ball of the invention, dimples are randomly arranged. Differently stated, regularity is eliminated from the arrangement of a plurality of dimples constituting a unit. As a result, the dimpled golf ball is improved in both aerodynamic performance and aerodynamic isotropy. The aerodynamic properties do not substantially differ among different points of impact. The ball covers equal distance regardless of the point of impact.
When a box containing a plurality of balls is vibrated, the balls pack randomly and closely. Simulating this phenomenon in a simplified manner on a computer, the dimple distributing method of the invention determines the final arrangement that satisfies the above converging condition. The method of the invention ensures that a golf ball having dimples randomly and closely arranged and exhibiting improved aerodynamic performance and aerodynamic isotropy is manufactured in a simple manner.
REFERENCES:
patent: 4720111 (1988-01-01), Yamada
patent: 4869512 (1989-09-01), Nomura et al.
patent: 4874169 (1989-10-01), Litchfield
patent: 5033750 (1991-07-01), Yamagishi et al.
patent: 5688194 (1997-11-01), Stiefel et al.
patent: 5772532 (1998-06-01), Stiefel et al.
Ihara Keisuke
Kasashima Atsuki
Maehara Kazuto
Bridgestone Corporation
Graham Mark S.
Hunter Alvin A
Sughrue Mion Zinn Macpeak & Seas, PLLC
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