Patent Application
20120015761
The invention relates in general to a golf ball, and more particularly, to an improved golf ball having multiple sets of identical hemispheres created by non-planar parting lines symmetrically arranged.
The usual golf ball manufacturing techniques include several different steps, depending on the type of ball, such as one, two, three or even more than three piece balls. In general, a solid or composite elastomeric core of one or more layers is made, and an outer dimpled cover is formed around the core.
There are several methods well known in the art for molding a cover over a core, including compression molding, injection molding, and casting. Irrespective of the method, the molding operation is accomplished by using a pair of generally hemispherical mold cavities, each of which has an array of protrusions machined or otherwise provided in its cavity, said protrusions forming the dimple pattern on the periphery of the golf ball during the cover molding operation.
When dimple protrusions are formed on the mold cavity surface, they are typically positioned between the equator and the pole of the resulting mold cavity. The parting line is typically machined after the dimple forming process. For ease of manufacturing, the parting line of the cavity is usually machined as a flat surface generally coinciding with the equator plane of the mold cavity. During the molding process, this provides positive shut off preventing flowing cover material from leaking out of the mold. This dimple positioning and flat parting line results in a great circle path on the ball that is essentially devoid of dimples. This is commonly referred to as the equator, parting line, or seam of the ball. Over the years dimple patterns have been developed to compensate for aesthetic and/or flight performance issues arising from the presence of the seam.
It is well known that the dimple pattern of a golf ball is a critical factor insofar as the flight characteristics of the ball are concerned. The dimples influence the aerodynamic lift and drag forces exerted on the golf ball which in turn strongly influence its overall performance and flight stability. When a golf ball is struck properly, it will spin about an axis and the interaction among the spin, the dimples and the oncoming air stream will produce the desired lift, drag, and flight characteristics.
In order for a golf ball to achieve optimum flight consistency, it is beneficial for its dimples to be arranged with multiple axes of symmetry. Otherwise, the ball might fly differently depending upon its orientation prior to being struck. Golf balls that include only a single dimple free equatorial parting line inherently are limited to only one symmetry axis. In order to achieve good flight consistency, it is often necessary to compensate for this limitation by adjusting the positions and/or dimensions and/or shapes of certain dimples. Alternatively, additional symmetry axes can be created by incorporating additional “false” parting lines. However, each false parting line is dimple free like the real one, so this practice tends to increase the amount of undimpled surface on the ball, resulting in reduced ball flight distance.
This problem can be solved by allowing dimples to intersect the equator, and using a non-planar (stepped, zig-zag, wavy, staggered, or otherwise corrugated) parting line that encircles the ball in the equator vicinity while skirting the dimples. Since this type of parting line does not necessarily increase the amount of undimpled surface, adding multiple false duplicates also need not increase the amount of undimpled surface. Some U.S. patents that seek to place dimples intersecting the equator of the ball include U.S. Pat. Nos. 6,200,232, 6,123,534 and U.S. Pat. No. 5,688,193 to Kasashima et al., U.S. Pat. No. 5,840,351 to Inoue et al., and U.S. Pat. No. 4,653,758 to Solheim. These patents introduced “stepped” and/or “zig zag” parting lines. While this could potentially improve the consistency and symmetry of flight performance, it does not sufficiently improve dimple coverage, since the parting lines include straight segments that do not permit tight dimple packing on opposite sides. A stepped path often results in a greater loss of dimple coverage than a straight path because it discourages interdigitation for a larger number of dimples
Efforts to improve dimple symmetry have explored the use of multiple parting lines and the resulting dimple patterns produced. U.S. Pat. Nos. 4,560,168 and 5,415,410 issued to Aoyama disclose the use of six and three great circle parting lines respectively. This produces multiple axes of symmetry, but there is a likely reduction of dimple coverage resulting from the multiple planar parting lines. U.S. Pat. No. 7,179,178 to Veilleux et al. teaches the use of three non-planar parting lines defining hexispheres. However, there is no provision for multiple axes of symmetry, nor are the six hemispheres produced by the three parting lines likely to be identical.
Therefore, a need exists for an improved golf ball combining a high degree of dimple coverage, multiple axes of symmetry, and multiple hemispheres that are substantially identical to each other.
The present invention relates to a golf ball produced by a mold that forms multiple symmetrically arranged non-planar parting lines to create multiple identical hemispheres. Whereas only one parting line is the real one, all of them create identical hemispheres that contain dimple patterns that are essentially identical relating to dimple shape, size, volume, distribution and location.
Each embodiment of the invention provides for a golf ball wherein the sum of all the volumes of the dimples lying predominantly above the equator is equal to the sum of all the volumes of the dimples lying predominantly below the equator.
An embodiment of the invention provides for at least three non-planar parting lines, one being a real parting line, and the remaining ones being false. This embodiment creates at least six substantially identical hemispheres.
An embodiment of the invention provides that the distance between the amplitude of a non-planar parting line and the equator of the ball is less than 53% of the largest dimple diameter, preferably less than 26% and more preferably less than 11%.
In the present invention, the number of identical non-planar parting lines is determined by the polyhedral geometry underlying the dimple pattern. For example, for an octahedron based dimple pattern the total number of real and false identical parting lines is three and the number of identical hemispheres is therefore six. For an icosidodecahedron dimple pattern, the total number of real and false identical parting lines is six and thus the number of identical hemispheres is twelve. For a cuboctahedron dimple pattern the total number of real and false parting lines is four and the number of identical hemispheres is eight. Other patterns have as many as ten total real and false identical parting lines and twenty identical hemispheres.
Most dimple patterns have a real parting line that delineates two substantially identical hemispheres. However, dimple patterns with additional matching false parting lines can have more than two such hemispheres and higher orders of symmetry. Some benefits of this include: more even dimple distribution; potential for higher packing efficiency; and improved methods to mask the real molded parting line of the ball. Further, it is anticipated that dimple patterns generated in this manner have improved stability and symmetry of flight as a result of the higher degree of dimple pattern symmetry. This concept has been noted before; however it has only been seen in prior art golf balls having flat parting lines and patterns that don't have the additional identical hemispheres. The present invention has provided a golf ball, not only with multiple identical non-planar parting lines and symmetry order greater than two, but wherein the dimples are arranged in such a way as to create more than two identical hemispheres and parting lines that maintain a functional relationship to the underlying polyhedral geometry.
Some dimple patterns contain false parting lines in an attempt to hide the manufacturing mold parting line on the golf ball, but these parting lines are merely similar in appearance. In the present invention, the false parting lines that are created are nominally exact replicas of the actual parting line. It is understood that the false parting lines are not physically present on the golf ball; rather they represent imaginary paths that are identical to the real parting line in shape and geometric relationship to neighboring dimples. The number and distribution of these parting lines is a by-product of the underlying geometry and method employed to develop these dimple patterns. The pattern is designed as follows:
(1)
(2) The parting line is such that the sum of the volumes of the dimples lying predominantly above the equator (VDA) is equal to the sum of the volumes of the dimples lying predominantly below the equator (VDB):
ΣVDA=ΣVDB Equation 1
A dimple is considered to lie predominantly above the equator 12 if its center point lies above the equator, and predominantly below the equator if its center point lies below the equator. For non-circular dimples, the center point is defined to be the centroid of the dimple.
(3) In order to maintain manufacturability as well as pattern symmetry, the maximum amplitude of the parting line (Ap) from equator 12 is at most 53% of the nominal design diameter of the largest dimple that is adjacent to the parting line (DMAX):
AP≦0.53(DMAX) Equation 2
Preferably,
AP≦0.26(DMAX) Equation 3
More preferably,
AP≦0.11(DMAX) Equation 4
For non-circular dimples, DMAX is the vertical span of the dimple (measured perpendicular to the equator) rather than the diameter.
(4) The staggered parting line is nominally exactly replicated so that it appears several times on the ball, and the total number of identical parting lines (NPL) follows Equation 5. This value depends upon the polyhedron used to define the pattern. An example using an octahedron layout is shown in
NPL≧3 Equation 5
(5) The dimple pattern is further defined such that any of the real or false parting lines on the ball splits the pattern into two nominally identical dimpled hemispheres (Hn & Hn+1), as seen in
(6) As stated above, the parting lines 14, 16, and 18 split the ball into six nominally identical hemispheres. This high degree of symmetry is anticipated to yield enhanced flight stability and aerodynamic consistency. It is understood that in certain situations, dimples that are nominally the same in shape, size, volume, distribution or location may not be precisely identical. This can result from manufacturing variations, especially related to paint coats or other finishing operations, from the presence of various manufacturing code markings in the dimples, or from variations due to molding techniques. For example, golf balls with injection molded covers typically include certain dimples in the polar regions (usually within 30° latitude from the pole) that have been slightly modified geometrically in order to accommodate retractable pins and vents. Specifically, circular dimples are often modified to a slightly elliptical shape. For the purposes of this invention, these dimples are considered to be nominally the same as their unmodified counterparts.
While
While it is apparent that the illustrative embodiments of the invention disclosed herein fulfill the objectives stated above, it is appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. Therefore, it will be understood that the appended claims are intended to cover all modifications and embodiments, which would come within the spirit and scope of the present invention. The dimple patterns of the present invention can be used with any type of golf ball with any playing characteristics. For example, the dimple pattern can be used with conventional golf balls, solid or wound. These balls typically have at least one core layer and at least one cover layer. Wound balls typically have a spherical solid rubber or liquid filled center with a tensioned elastomeric thread wound thereon. Wound balls typically travel a shorter distance, however, when struck as compared to a two piece ball. The cores of solid balls are generally formed of a polybutadiene composition. In addition to one-piece cores, solid cores can also contain a number of layers, such as in a dual core golf ball. Covers, for solid or wound balls, are generally formed of ionomer resins, balata, or polyurethane, and can consist of a single layer or include a plurality of layers and, optionally, at least one intermediate layer disposed about the core.
All of the patents and patent applications mentioned herein by number are incorporated by reference in their entireties.
While the preferred embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
