GOLF CLUB HEAD

Abstract

This invention provides a golf club head having a plurality of grooves formed in a face thereof. Edges of the groove are rounded with a radius of not more than 0.2 mm. A width W (mm) of the groove measured with the rounded edge being included, a width Ws (mm) between the grooves adjacent to one another, a width Wr (mm) of the groove measured based on the 30 degrees measurement rule and a cross section area S (mm2) of the groove satisfy the following expressions; W/Ws×100≧35(%), S/(Ws×0.5)×100≅70(%).

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf club head, and particular to a groove formed on the face thereof.

2. Description of the Related Art

It is provided on a face of a golf club head plurality of grooves, called marking line, score line or face line grooves. These grooves affect an amount of spin of a ball. In the case of the golf club head of an iron club, especially the wedge, it is desirable to form the grooves in order to increase the amount of spin of a ball.

Japanese Patent Application Laid-Open No. 9-19974 discloses a golf club having grooves of V-shaped or trapezoidal cross section. Japanese Patent Application Laid-Open No. 9-70457 and No. 10-179824 disclose a golf club head having grooves edges (boundary portions between side surfaces of the grooves and a face)of which are rounded. This rounding has an effect of preventing a golf ball from getting damaged (for example, scratches and the like). Japanese Patent Application Laid-Open No. 2003-93560 and No. 2005-287534 disclose a golf club head having grooves each of which has a side surface formed not by a single surface, but by two differently angled surfaces. In Japanese Patent No. 3463779, a set of iron type golf clubs each of which has a grooved area ratio to the face set differently depending on its own type number of golf clubs is disclosed. Incidentally, a golf club head used in the official games is subject to constraints on a width and depth of the groove, and a pitch between the adjacent grooves specified in the rules, and therefore, in consideration of applications in the official games, it is required to design a golf club head in a range to meet the rules.

Now, an amount of spin of a golf ball in the rain or hitting a shot in the rough tends to be smaller than that with out the rain or hitting on the fairway. A method for prevention of a decrease in the amount of spin of a ball includes sharpening the angle of a groove edge. However, a decrease in the angle of the groove edge may cause a ball to be easily damaged.

Rounding of the groove edge as the golf club head disclosed in Japanese Patent Application Laid-Open No. 9-70457 and No. 10-179824 allows ball damage to be reduced, but the amount of spin of a ball is also decreased.

SUMMARY OF THE INVENTION

The present invention has been made in order to overcome the deficits of prior art.

According to the aspects of the present invention, it is provided a golf club head having a plurality of grooves formed on a face thereof, wherein edges of the groove are rounded with a radius of not more than 0.2 mm, and a width W (mm) of the groove measured with the rounded edge being included, a width Ws (mm) between the grooves adjacent to one another, a width Wr (mm) of the groove measured based on the 30 degrees measurement rule and a cross section area S (mm²) of the groove satisfy the following expressions; W/Ws×100≧35(%), S/(Ws×0.5)×100≧70(%).

In this golf club head, rounding of the groove edge with a radius being not more than 0.2 mm prevents a ball from getting damaged. While, setting of “W/Ws×100” given above which is representative of an area ratio of a grooved area in the face and “S/(Wr×0.5)×100” given above which is representative of an amplitude of the volume of the groove to the values above described, along with balancing between the area ratio of the grooved area and the amplitude of the volume, allows a large decrease in the amount of spin of a ball to be avoided in the rain or a shot in the rough.

Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a general view of a golf club head 1 according to one embodiment of the present invention;

FIG. 1B is a cross sectional view of a groove 20;

FIG. 2A is an explanatory diagram when an edge of the groove 20 is rounded;

FIG. 28 is a schematic diagram illustrative of a cross sectional area ratio;

FIG. 2C is a schematic diagram illustrative of the 30 degrees measurement rule;

FIG. 3 shows the experimental conditions and the experimental result of examples of the present invention and comparative examples; and

FIG. 4A to 4C show the experimental result of the examples of the present invention and the comparative examples.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.

FIG. 1A is a general view of a golf club head 1 according to one embodiment of the present invention. In FIG. 1A, an example is shown when the present invention is applied to an iron type golf club head. The present invention is suitable for the golf club heads especially for a wedge such as a sand wedge, a pitching wedge or an approach wedge for which a large amount of spin of a ball is required. However, the present invention is also applicable to the golf club head for a wood golf club or a utility golf club.

The golf club head 1 has a plurality of grooves 20 formed on a face 10 thereof. In this embodiments each of the grooves 20 is a straight groove extending in toe-to-heel direction and each pitch between the grooves 20 adjacent to one another is arranged to be equal (each pitch has the same length). FIG. 1B is a cross sectional view of the groove 20 taken in the direction perpendicular to the longitudinal direction (toe-to-heel direction) thereof and shows the two adjacent grooves 20. In this embodiment, the groove 20 has the same cross section shape in the longitudinal direction except for both distal ends thereof. Further, each of the plurality of grooves 20 has the same cross section shape.

The groove 20 has a pair of side surfaces 21 and 22, and a bottom surface 23 is trapezoidal in cross section. In this embodiment, the cross section shape of the groove 20 is symmetric about the center line CL thereof. Each of the pair of the side surfaces 21 and 22 comprises a flat surface (a straight line in cross section) leading to the face 10 at the upper side and leading to the bottom surface 23 at the lower side. An angle θ corresponds to an angle between the side surfaces 21 and 22. The bottom surface 23 is parallel to the face 10. Although, in this embodiment, the cross section shape of the groove 20 is trapezoidal, it can be rectangular, square and triangular.

Edges 24 of the groove 20 are rounded. A radius for rounding the edge 24 is not more than 0.2 (mm). This rounding provides an effect to prevent a ball from getting damaged (scratches and the like). The radius for rounding is preferably equal to or more than 0.05 (mm), and not more than 0.1 (mm).

The groove 20 has a bottom width Wb, a depth D and a width W. Further, a width Ws is defined between the grooves 20 adjacent to one another. The bottom width Wb indicates a distance between both ends of the bottom surface 23. The depth D indicates a distance from the face 10 to the bottom surface 23. The width W is a width of the groove 20 in the direction perpendicular to the longitudinal direction thereof. The width W, as shown in FIG. 2A, means a width which is measured with the roundness (a radius r) of the edges 24 of the groove 20 being included and which is to be measured from the starting point to get rounded (the position shown by a broken line in FIG. 2A). The width Ws indicates a distance between the starting points to get rounded (the position shown by a broken line in FIG. 2A) of the two adjacent grooves 20.

The term “groove width measured with the roundness being included” used herein means the width W measured by the method above described, and the width W is distinguished from a width which is measured based on so-called the 30 degrees measurement rule in the R&A regulation which is a method for measuring a groove width for a glf club head used of official games. As shown in FIG. 2C, under the 30 degrees measurement rule, a distance between points at which imaginary lines L forming 30 degrees from the face 10 contact with the side surfaces 21 and 22 of the groove 20 respectively is measured as a width (Wr) of the groove 20. The width measured based on the 30 degrees measurement rule hereinafter is called “rule-based width”. When the edge 24 of the groove 20 is rounded as in this embodiment, the width W of the groove 20 may be different from the rule-based width Wr. However, when the edges of the groove 20 are not rounded, the width W of the groove 20 conforms to the rule-based width Wr.

Further, the rule-based width Wr is stipulated to be not more than 0.9 (mm). The depth D of the groove is also stipulated in the rules to be not more than 0.5 (mm). Moreover, the pitch of the grooves (a distance between the center lines CL of the grooves) is stipulated in the rules to be equal to or more than “the rule-based width” (Wr: mm)×4.

Next, the larger the cross section area of the groove 20 is, the larger the volume of the groove 20 becomes. In this embodiment, a cross section area ratio as an evaluation indicator of an amplitude of the cross section area of the groove 20, i.e. an amplitude of the volume of the groove 20 will be proposed as described below. As described previously, the depth D of the golf club head for the official games is stipulated in the rules to be not more than 0.5 (mm). Therefore, when edges of the groove 20 are not rounded and the rule-based width Wr is applied to the groove 20, the largest cross section area of the groove 20 is Wr (mm)×0.5 (mm)=0.5 Wr (mm²), as shown in the right side of FIG. 2B.

Now, the cross section area ratio of the cross section area S (mm²) of the groove 20 (see the left side of FIG. 2B) to this largest cross section area can be an evaluation indicator which represents the amplitude of the volume of the groove 20. The cross section area ratio is expressed in the following expression (1):

The cross section area ratio (%)=S/(Wr×0.5)×100   expression (1)

Next, an area ratio of a grooved area of the groove 20 in the face 10 affects the amount of spin of a ball. In this embodiment, an area ratio derived from the following expression (2), as an indicator of the area ratio of the grooved area, will be proposed.

The grooved area ratio (%)=W/Ws×100   expression (2)

In the golf club head 1 of this embodiment, forming the rounding of the edge 24 of the groove 20 with the radius of not more than 0.2 mm prevents a ball from getting damaged. Further, balancing between the grooved area ratio of the groove 20 specified in the expression (2) given above and the cross section area ratio of the groove 20 specified in the expression (1) given above allows a large decrease in the amount of spin of a ball to be avoided in the rain or a shot in the rough. In this embodiment, the grooved area ratio of the groove 20 given above is set equal to or more than 35%, and the cross section area ratio of the groove 20 given above is set equal to or more than 70%.

EXAMPLE

FIG. 3 shows the experimental result of measurement of a degree of ball damage (a degree of scratches) and the amount of spin of a ball with specifications of the grooves being varied for examples 1 to 5 of the present invention and comparative examples 1 to 7 as conventional examples. The experiments were performed by using a sand wedge with a loft angle of 56 degrees, providing the grooves in the sand wedge to which grooves different specifications were applied, and hitting unused balls by the sand wedge driven by a robot machine. The head speed of the sand wedge was set to 40 (m/s). Also, taking cases of shots in clear weather and cases of shots in the rain or in the rough into consideration, for the dry face (dry) and for the face covered with a thin wet paper (wet), ten balls were hit, respectively.

In FIG. 3, “Groove specifications” show specifications of grooves of the comparative examples and the examples. In any of the comparative examples and the examples, the cross section shape of the groove is trapezoidal as shown in FIG. 1B. “Angle θ” is an angle formed between the side surfaces (see the angle θ in FIG. 1B). “Radius for rounding” represents a radius for rounding the groove edge. In the comparative examples 1 to 3, the groove edge is not rounded. “Groove width W” is the groove width which was explained with reference to FIG. 2A and is to be measured including the roundness. “Rule-based width Wr” is the groove width measured based on the 30 degrees measurement rule.

“Width Ws between the grooves” is the width Ws explained with reference to FIG. 2A. “Pitch” is a distance between the center lines (the center line CL shown in FIG. 1B) of the adjacent grooves. “Grooved area ratio” is the grooved area ratio above described calculated by using the expression (2) above. “Groove depth D” is a distance from the face to the bottom surface of the groove. “Cross section area S” is the cross section area of the groove. “Cross section area ratio” is the cross section area ratio above described calculated by using the expression (1) above.

Next, in the experimental result, “Degree of scratches” was evaluated in 1-to-10 scale by the three persons who observed visually and tactilely the degree of damage incurred on the surface of a ball after hitting in the case of the dry face (dry). In this experiment, “10” was assigned to the largest degree of damage incurred on the surface of the ball and “1” was assigned to the smallest degree of damage. “Amount of spin” was derived from change in the position of an indicator marked in advance on the surface of a ball measured by video recording of the ball upon impact. The amount of spin is an average value of ten shots, for the dry face (dry) and for the wet face (wet), respectively.

“Rule conformity” shows whether the golf club heads used in the comparative examples 1 to 7 and the examples 1 to 5 conform to the rules applied to the golf club head for the official games or not. Only the comparative example 3 does not conform to the rules as regarding the pitch.

FIG. 4A is a bar graph plotted for illustrating the degree of scratches in the experimental result shown in FIG. 3. FIG. 4B is a graph plotted for illustrating relation between “Grooved area ratio” and “Amount of spin” of the experimental result shown in FIG. 3 in a separate form for the dry face (dry) and for the wet face (wet). FIG. 4C is a graph plotted for illustrating relation between “Cross section area ratio” and “Amount of spin” of the experimental result shown in FIG. 3 in a separate form for the dry face (dry) and for the wet face (wet).

Then, focusing attention on the degree of scratches, a large degree of scratches is found in the comparative examples 1 to 3 in which the angle θ is small and the groove edges are not rounded. Therefore, rounding of the groove edges have an effect to prevent a ball from getting damaged.

Next, studying “Amount of spin”, the comparative examples 2 and 3, even in the wet case, have a large amount of spin, and especially for the comparative example 3, the amount of spin in the wet case exceeds that in the dry case. However, since the comparative examples 2 and 3 have a bad “Degree of scratches” described above, they are lack in practicality.

Although the comparative examples 1 and 4 have a comparatively large “Cross section area ratio” (each has that of equal to or more than 70%), a large decrease in the amount of spin in the wet case relative to the dry case is found. This may be conceivably due to smallness of “Grooved area ratio” (10% and 25%, respectively). Although the example 1 has the smallest “Grooved area ratio” among the examples 1 to 5 (38%), it has a smaller decrease in the amount of spin in the wet case, compared to the comparative example 1 and 4.

However, the comparative examples 5 to 7 have a comparatively large “Grooved area ratio”, while, a large decrease in the amount of spin in the wet case relative to the dry case is found. This may be conceivably due to smallness of “Cross section area ratio” (59%, 63% and 50%, respectively). Although the example 3 and 5 have the smallest “Cross section area ratio” among the examples 1 to 5 (70%), they have a smaller decrease in the amount of spin in the wet case, compared to the comparative examples 5 to 7.

Based on the foregoing experimental result, it can be seen that the amount of spin in the wet case is improved by well-balancing between “Grooved area ratio” and “Cross section area ratio”. Further, it is considered, judging from “Grooved area ratio” and “Cross section area ratio” of the examples 1 to 5, that setting of “Grooved area ratio” to equal to or more than 35% and “Cross section area ratio” to equal to or more than 70% may allow the golf club head having a small decrease in the amount of spin in the wet case to be achieved.

Further, when the golf club head of the present invention is used in the regular games, it is required that the rule-based width Wr is not more than 0.9 (mm). However, the narrower the rule-based width Wr is, the smaller the cross section area of the groove becomes. In the example 3, although the rule-based width Wr is set to 0.6 (mm), a larger decrease in the amount of spin in the wet case is not found, compared to those of the examples 1, 2, 4 and 5. Therefore, the rule-based width Wr of the golf club head according to the present invention is preferably equal to or more than 0.6 (mm) and not more than 0.9 (mm).

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2006-214852, filed on Aug. 7, 2006 which is hereby incorporated by reference herein in their entirety.

Claims

1. A golf club head having a plurality of grooves formed on a face thereof, wherein

edges of said groove are rounded with a radius of not more than 0.2 mm, and

a width W (mm) of said groove measured with said rounded edge being included, a width Ws (mm) between said grooves adjacent to one another, a width Wr (mm) of said groove measured based on the 30 degrees measurement rule and a cross section area S (mm2) of said groove satisfy the following expressions: W/Ws×100≧35(%) S/(Ws×0.5)×100≧70(%).

2. The golf club head according to claim 1, wherein

said width Wr is equal to or more than 0.6 (mm) and not more than 0.9 (mm).