Golf ball and method of arranging dimples thereto

Details Golf ball and method of arranging dimples thereto Golf ball and method of arranging dimples thereto

1999-09-15

2001-03-13

Graham, Mark S. (Department: 3711)

Games using tangible projectile

Golf

Ball

C473S383000, C473S379000, C473S381000, C473S382000

Reexamination Certificate

active

06200232

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a dimpled golf ball free of a great circle which does not intersect with the dimples and having high symmetry. It also relates to a method of arranging dimples to the surface of a golf ball.
2. Prior Art
The flight performance of golf balls is greatly affected by the arrangement and configuration (including diameter, depth and cross-sectional shape) of dimples. Various dimple arrangements are known in the art for arranging a plurality of dimples on the ball surface in an even or dense fashion. Typical known dimple arrangements are polyhedral arrangements including octahedral, cubic-octahedral, dodecahedral and icosahedral arrangements.
JP-B 7875/1994 attemps to tailor the dimple configuration such that the overall effective volume of dimples remains substantially equal between pole hitting (the spin axis is in the equator plane) and seam hitting (the spin axis is a pole-to-pole line).
Golf balls are generally molded in an axisymmetric manner by using a mold comprising a pair of mold halves, removably mating them along a parting line to define a spherical cavity therein, and introducing stock material into the cavity. The thus molded golf balls tend to have a higher degree of roundness or spherically about a pole-to-pole axis corresponding to a line connecting the apexes of the mold half cavities, but a lower degree of roundness about an axis on a plane circumscribed by a seam line corresponding to the parting plane of the mold. Because of such variation in roundness, conventional golf balls exhibit different flight performance depending on the position at which the ball is hit. Such flight performance variation raises a serious problem in the game of golf wherein the Rules of Golf prescribe that “the ball shall be played as it lies, except as otherwise provided in the Rules.”
More specifically, when a golf ball is hit by a club, the ball is given back spin although the number of revolutions varies with a particular type of club. The hitting of the ball is generally classified into pole hitting and seam hitting depending on an impact point. Reference is now made to FIGS.
8
(A) and
8
(B) wherein a golf ball
11
has a seam line
12
and a center
16
. The term “pole hitting” means that the ball
11
is hit at arrow
20
to give back spin about a straight line
18
connecting two diametrically opposed points
14
,
14
on the seam line
12
and the center
16
as shown in FIG.
8
(A). The term “seam hitting” means that the ball
11
is hit at arrow
26
to give back spin about a straight line
24
extending perpendicular to a circular plane
22
circumscribed by the seam line
12
and passing the center
16
as shown in FIG.
8
(B). As previously mentioned, in the event of pole hitting shown in FIG.
8
(A), the ball is susceptible to extra lift or drag since it does not define a true circle about the spin axis
18
. On the other hand, in the event of seam hitting shown in FIG.
8
(B), the ball is substantially free of extra lift or drag since it is close to a true circle about the spin axis
24
. As a consequence, if the ball is simply designed such that the effect of dimples may be equal between pole hitting and seam hitting, the effect of dimples would be greater upon pole hitting because of a deviation from roundness. Then on pole hitting, the golf ball receives extra lift or drag, exhibiting different flight performance than on seam hitting. This means that the flight performance varies with respect to a particular position where the golf ball is hit.
To produce a golf ball which is improved in symmetry in that the flight performance remains constant regardless of a particular hit position, the arrangement and configuration of dimples must be designed in consideration of the shape or roundness of the ball to optimize the effect of dimples. This requirement has not been fully satisfied.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a golf ball having dimples in an octahedral, dodecahedral or icosahedral arrangement which is improved in symmetry in that the ball will follow the same trajectory on either seam hitting or pole hitting, that is, the flight performance does not vary with a particular hit position and which can be conveniently molded using a split mold.
Another object of the present invention is to provide a method of arranging dimples on the surface of a golf ball to improve symmetry.
According to one aspect of the present invention, there is provided a golf ball which is molded in a mold comprising a pair of mold sections which are removably joined to define a spherical cavity therein whereby the golf ball has a parting line at the junction between the mold sections, the golf ball having two to six types of dimples having different diameters within a range of 1.8 to 5 mm on the surface thereof, the dimples being arranged in a polyhedral arrangement selected from octahedral, dodecahedral and icosahedral arrangements so that the golf ball is free of a great circle which does not intersect with the dimples and some of the dimples lie across the parting line, wherein off-center-crossing dimples which lie across the parting line and whose center lies outside the parting line are shifted upward or downward from the parting line or reduced in diameter so that the off-center-crossing dimples do not lie across the parting line, while center-crossing dimples whose center lies on the parting line are kept unchanged, and the surface coverage of dimples is at least 71%.
According to another aspect of the present invention, there is provided a method of arranging two to six types of dimples having different diameters within a range of 1.8 to 5 mm on the surface of a golf ball which is molded in a mold comprising a pair of mold sections which are removably joined to define a spherical cavity therein so that the surface coverage of the dimples is at least 71%, the golf ball having a parting line formed at the junction between the mold sections and some of the dimples lying across the parting line, the method comprising arranging the dimples in a polyhedral arrangement selected from octahedral, dodecahedral and icosahedral arrangements so that the golf ball is free of a great circle which does not intersect with the dimples, and shifting off-center-crossing dimples which lie across the parting line and whose center lies outside the parting line upward or downward from the parting line or reducing the off-center-crossing dimples in diameter so that the off-center-crossing dimples do not lie across the parting line, while center-crossing dimples whose center lies on the parting line are kept unchanged.
A variety of golf balls having dimples lying across the parting line and free of a great circle which does not intersect with the dimples are known in the art. These balls are believed to have higher symmetry than golf balls having no dimples lying across the parting line. On the other hand, the symmetry of these balls also depends on the dimple arrangement. From the standpoint of symmetry, octahedral, dodecahedral and icosahedral arrangements are appropriate. When dimples are arranged in a polyhedral arrangement in the prior art, it is a common practice to arrange the dimples so that they may not lie across the parting line.
From the above viewpoint, if dimples are distributed according to the polyhedral arrangement to achieve a high degree of symmetry while increasing the number or diameter of dimples so that the surface coverage of the dimples may be 71% or more, then the number of dimples lying across the parting line becomes as many as 20 or more. For molding such golf balls having dimples lying across the parting line using a split mold, there are known several techniques. For example, parting surfaces of upper and lower mold sections are corrugated at positions where the crossing dimples are to be formed, and dimple-forming protrusions are provided on the inner surface of the convex corrugations; or parting surfaces of upper and lower mold sections are formed

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