U.S. patent application number 11/414292 was filed with the patent office on 2007-01-18 for method of designing golf club and golf club head.
This patent application is currently assigned to SRI Sports Limited. Invention is credited to Masayoshi Nishio, Masaya Tsunoda.
Application Number | 20070015601 11/414292 |
Document ID | / |
Family ID | 37662286 |
Filed Date | 2007-01-18 |
United States Patent
Application |
20070015601 |
Kind Code |
A1 |
Tsunoda; Masaya ; et
al. |
January 18, 2007 |
Method of designing golf club and golf club head
Abstract
A method for designing a golf club head by using a computer. A
golf club head model in which the rear surface of a face part is
provided with reinforcing ribs and a golf ball model to be analyzed
by using a finite element method (FEM) are prepared. Conditions
including the positions of the reinforcing ribs and the
configurations thereof including the sectional areas and heights
are adjusted to set the maximum value of the Mises stresses
generated by the collision between the golf ball model and the golf
club head model at any off-center positions of said front surface
of said face part thereof to less than 1.3 times the maximum value
of the Mises stress generated by the collision between the golf
ball model and the golf club head model at the center of said front
surface of said face part thereof.
Inventors: |
Tsunoda; Masaya; (Hyogo,
JP) ; Nishio; Masayoshi; (Hyogo, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
SRI Sports Limited
|
Family ID: |
37662286 |
Appl. No.: |
11/414292 |
Filed: |
May 1, 2006 |
Current U.S.
Class: |
473/346 |
Current CPC
Class: |
A63B 53/045 20200801;
A63B 60/00 20151001; A63B 53/0466 20130101; A63B 53/0458 20200801;
A63B 53/0408 20200801; A63B 53/04 20130101; A63B 53/0454 20200801;
A63B 53/0416 20200801; G06F 30/23 20200101 |
Class at
Publication: |
473/346 |
International
Class: |
A63B 53/00 20060101
A63B053/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 12, 2005 |
JP |
2005-202727 |
Claims
1. A method of designing a golf club head by using a computer,
comprising the steps of: preparing a ball model and a club head
model obtained by dividing a golf ball and a golf club head into a
plurality of finite elements respectively, wherein said club head
model is provided with a central reinforcing rib formed at a
central portion of a rear surface of a face part thereof and a
plurality of belt-shaped reinforcing ribs extended radially from
said central reinforcing rib toward a peripheral edge of said rear
surface of said face part; executing simulation of collision
between said ball model and said club head model at a plurality of
positions of a front surface of said face part thereof to determine
a Mises stress generated at each of said collision positions; and
changing setting conditions of said central reinforcing rib and
said belt-shaped reinforcing ribs to set a maximum value of Mises
stresses generated at off-center positions of said front surface of
said face part to less than 1.3 times a maximum value of a Mises
stress generated at a center of said front surface of said face
part.
2. The method according to claim 1, wherein not less than four nor
more than 10 belt-shaped reinforcing ribs are formed on said rear
surface of said face part; and said setting conditions of said
belt-shaped reinforcing ribs include a number of said belt-shaped
reinforcing ribs, positions thereof, sectional areas thereof,
heights thereof, and widths thereof.
3. The method according to claim 1, wherein said club head model is
a wood club head model; said reinforcing ribs are formed on a rear
surface of a metal plate forming said face part; and when said
maximum value of said Mises stresses generated by said collision
between said ball model and said club head model at said off-center
positions of said front surface of said face part is not less than
1.3 times said maximum value of said Mises stress generated by said
collision between said ball model and said club head model at said
center of said front surface of said face part, said sectional
area, said width or/and said height of said reinforcing ribs,
disposed on said rear surface of said face part, which correspond
to said off-center positions are set large, whereas when said ratio
is less than 1.0, said sectional area, said width or/and said
height of said reinforcing ribs, disposed on said rear surface of
said face part, which correspond to said off-center positions are
set small.
4. The method according to claim 2, wherein said club head model is
a wood club head model; said reinforcing ribs are formed on a rear
surface of a metal plate forming said face part; and when said
maximum value of said Mises stress generated by said collision
between said ball model and said club head model at said off-center
positions of said front surface of said face part is not less than
1.3 times said maximum value of said Mises stress generated by said
collision between said ball model and said club head model at said
center of said front surface of said face part, said sectional
area, said width or/and said height of said reinforcing ribs,
disposed on said rear surface of said face part, which correspond
to said off-center positions are set large, whereas when said ratio
is less than 1.0, said sectional area, said width or/and said
height of said reinforcing ribs, disposed on said rear surface of
said face part, which correspond to said off-center positions are
set small.
5. The golf club head designed by a designing method according to
claim 1.
6. A golf club head, wherein a central reinforcing rib is formed at
a central portion of a rear surface of a face part and not less
than four nor more than 10 belt-shaped reinforcing ribs are
extended radially from said central reinforcing rib toward a
peripheral edge of said rear surface of said face part; and a
maximum value of Mises stresses generated by collision between a
golf ball and said golf club head at off-center positions of a
front surface of said face part is set to less than 1.3 times a
maximum value of a Mises stress generated by collision between said
golf ball and said golf club head at a center of said front surface
thereof.
7. A golf club head in which a central reinforcing rib is formed at
a central portion of a rear surface of a face part and not less
than four nor more than 10 belt-shaped reinforcing ribs are
extended radially from said central reinforcing rib toward a
peripheral edge of said rear surface of said face part; a ratio
(W/t) of a width W of each of said belt-shaped reinforcing ribs to
a height t thereof is set to not less than 15 nor more than 40; and
each of said belt-shaped reinforcing ribs forms an intersection
angle of not less than 100 degrees nor more than 160 degrees with
respect to a reference plane of said rear surface of said face
part.
8. The golf club head according to claim 5, wherein said
reinforcing ribs are formed on a rear surface of a metal plate
composing said face part; and a sectional area of said central
reinforcing rib is set to not less than 20% nor more than 90% of an
area of an entire rear surface of said face part.
9. The golf club head according to claim 6, wherein said
reinforcing ribs are formed on a rear surface of a metal plate
composing said face part; and a sectional area of said central
reinforcing rib is set to not less than 20% nor more than 90% of an
area of an entire rear surface of said face part.
10. The golf club head according to claim 7, wherein said
reinforcing ribs are formed on a rear surface of a metal plate
composing said face part; and a sectional area of said central
reinforcing rib is set to not less than 20% nor more than 90% of an
area of an entire rear surface of said face part.
11. The golf club head according to claim 8, wherein a thickness of
said central reinforcing rib is set to not less than 2.6 mm nor
more than 5.0 mm; and an area of said central reinforcing rib is
set to not less than 10 mm.sup.2 nor more than 1000 mm.sup.2.
12. The golf club head according to claim 9, wherein a thickness of
said central reinforcing rib is set to not less than 2.6 mm nor
more than 5.0 mm; and an area of said central reinforcing rib is
set to not less than 10 mm.sup.2 nor more than 1000 mm.sup.2.
13. The golf club head according to claim 10, wherein a thickness
of said central reinforcing rib is set to not less than 2.6 mm nor
more than 5.0 mm; and an area of said central reinforcing rib is
set to not less than 10 mm.sup.2 nor more than 1000 mm.sup.2.
14. The golf club head according to claim 5, wherein a portion
where said adjacent belt-shaped reinforcing ribs intersect with
each other is rounded; and a ratio (.theta./R) of an intersection
angle .theta. (degree) formed between said adjacent belt-shaped
reinforcing ribs to a radius of curvature R (mm) of said rounded
portion is set to not less than three nor more than 50.
15. The golf club head according to claim 6, wherein a portion
where said adjacent belt-shaped reinforcing ribs intersect with
each other is rounded; and a ratio (.theta./R) of an intersection
angle .theta. (degree) formed between said adjacent belt-shaped
reinforcing ribs to a radius of curvature R (mm) of said rounded
portion is set to not less than three nor more than 50.
16. The golf club head according to claim 7, wherein a portion
where said adjacent belt-shaped reinforcing ribs intersect with
each other is rounded; and a ratio (.theta./R) of an intersection
angle .theta. (degree) formed between said adjacent belt-shaped
reinforcing ribs to a radius of curvature R (mm) of said rounded
portion is set to not less than three nor more than 50.
17. The golf club head according to claim 8, wherein a portion
where said adjacent belt-shaped reinforcing ribs intersect with
each other is rounded; and a ratio (.theta./R) of an intersection
angle .theta. (degree) formed between said adjacent belt-shaped
reinforcing ribs to a radius of curvature R (mm) of said rounded
portion is set to not less than three nor more than 50.
18. The golf club head according to claim 11, wherein a portion
where said adjacent belt-shaped reinforcing ribs intersect with
each other is rounded; and a ratio (.theta./R) of an intersection
angle .theta. (degree) formed between said adjacent belt-shaped
reinforcing ribs to a radius of curvature R (mm) of said rounded
portion is set to not less than three nor more than 50.
Description
[0001] This nonprovisional application claims priority under 35
U.S.C. .sctn.119(a) on Patent Application No(s). 2005-202727 filed
in Japan on Jul. 12, 2005, the entire contents of which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of designing a
golf club head by utilizing a computer. The present invention also
relates to a golf club head. More particularly, the present
invention relates to a method of efficiently designing a golf club
head having a sufficient strength and excellent restitution
characteristics. To do so, a golf ball model and a golf club head
model both composed of a plurality of finite elements are used.
Further reinforcing ribs are formed on the rear surface of the face
part of the golf club head model. By changing conditions of the
reinforcing ribs, ball-hitting simulation is executed to make
stresses generated at any hitting positions of the face part
uniform.
[0004] 2. Description of the Related Art
[0005] Conventionally, a metal plate is disposed on the face part
of a wood head of a golf club. To improve the restitution
characteristic of the wood head at the time when a golf ball is hit
with the wood head, it is effective to thin the metal plate
disposed on the face part of the wood head to approximate the
natural frequency of the face part to that of the golf ball, based
on an impedance matching theory.
[0006] Therefore in recent years, there is a tendency for the face
part to be thinned. However, thinning the face part causes the
strength of the wood head to be low. Thus as a method of thinning
the face part and enhancing the strength of the face part, a method
of providing the rear surface of the face part with a reinforcing
rib is adopted.
[0007] For example, in the golf club head disclosed in Japanese
Patent Application Laid-Open No. 2003-290396 (patent document 1), a
plurality of reinforcing ribs is vertically mounted on the rear
surface of the face part, with the reinforcing ribs becoming
gradually lower toward the toe and the heel and longitudinally
equal or gradually higher toward the bottom (sole) of the golf club
head.
[0008] Because all the reinforcing ribs extend vertically in the
golf club head disclosed in the patent document 1, the reinforcing
ribs disposed at the toe and the heel make the rigidity of the face
part excessively high. Thus at the time of collision between a golf
ball and the face part, the face part is excessively restrained
from vibrating, thus having insufficient restitution performance.
In addition, although the reinforcing ribs have a large volume
(weight), they provide the face part with an insufficient
reinforcing effect.
[0009] In designing the golf club head, it is desirable to provide
it with a high degree of strength and a possible highest
restitution performance. The conventional method of designing the
golf club head depends greatly on experience and perception and
requires immense trial-and-error investigations. Thus it takes much
time to design the golf club head. In addition, there is a
variation in the guiding principle in designing the golf club head.
Therefore various proposals for efficiently designing the golf club
head excellent in various properties such as the restitution
performance, strength, and the like have been made.
[0010] For example, as disclosed in Japanese Patent Application
Laid-Open No. 9-149954 (patent document 2), the present applicant
proposed the following method serviceable for designing the golf
club head: The three-dimensional configuration of the golf club
head is measured by using a three-dimensional configuration
measuring apparatus. Based on the data of measured
three-dimensional configuration, the golf club head model is formed
by using a finite element method (FEM) and a construction-analyzing
pre-program. By using an analyzing software commercially available,
the inertial main shaft of the golf club head model and the main
inertial moment thereof are computed.
[0011] In the above-described designing method, the inertial main
shaft and the main inertial moment of the golf club head model in
the initial configuration thereof are computed to make them
serviceable for designing the golf club head. However, the method
has room for improvement in designing the golf club head having a
high restitution characteristics and strength.
[0012] Patent document 1: Japanese Patent Application Laid-Open No.
2003-290396
[0013] Patent document 2: Japanese Patent Application Laid-Open No.
9-149954
SUMMARY OF THE INVENTION
[0014] The present invention has been made in view of the
above-described problems. Therefore it is an object of the present
invention to provide a method of efficiently designing a golf club
head having a sufficient strength and a superior restitution
characteristic. To achieve the above-described object, a golf ball
model and a golf club head model are used. The rear surface of the
face part of the golf club head model is provided with reinforcing
ribs. In addition, a finite element method is used to make stresses
generated at different hitting positions of the face part
uniform.
[0015] To achieve the above-described object, the present invention
provides a method of designing a golf club head by using a
computer. The designing method includes the steps of preparing a
ball model and a club head model obtained by dividing a golf ball
and a golf club head into a plurality of finite elements
respectively. The club head model is provided with a central
reinforcing rib formed at a central portion of a rear surface of a
face part thereof and a plurality of belt-shaped reinforcing ribs
extended radially from the central reinforcing rib toward a
peripheral edge of the rear surface of the face part. The designing
method further includes the step of executing simulation of
collision between the ball model and the club head model at a
plurality of positions of a front surface of the face part thereof
to determine a Mises stress generated at each of the collision
positions; and the step of changing setting conditions of the
central reinforcing rib and the belt-shaped reinforcing ribs to set
a maximum value of Mises stresses generated at off-center positions
of the front surface of the face part to less than 1.3 times a
maximum value of a Mises stress generated at a center of the front
surface of the face part.
[0016] In the above-described construction, by using the golf ball
model and the golf club head model divided into a plurality of
finite elements respectively, conditions including the positions of
the reinforcing ribs, and the configurations thereof including the
sectional areas and heights are inputted to the computer to execute
ball-hitting simulation. Approximation of the stress generated by
the collision between the ball model and the golf club head model
at an arbitrary off-center position of the front surface of the
face part to the stress generated by the collision therebetween at
the center of the front surface thereof is set as the objective
function. The positions of the reinforcing ribs and the sectional
areas and heights thereof are set as the design variables. Thereby
the maximum Mises stress generated by the collision between the
golf ball model and the golf club head model at the center of the
front surface of the face part thereof and the maximum Mises stress
generated by the collision between the golf ball model and the golf
club head model at the arbitrary off-center position of the front
surface of the face part are compared with each other.
[0017] Owing to the comparison, the conditions of the positions of
the reinforcing ribs and the configurations thereof including the
sectional areas and heights are adjusted to set the maximum value
of the Mises stresses generated by the collision between the golf
ball model and the golf club head model at any off-center positions
to less than 1.3 times the maximum value of the Mises stress
generated by the collision between the golf ball model and the golf
club head model at the center.
[0018] As described above, as the reinforcing rib to be formed on
the rear surface of the face part, there are formed the central
reinforcing rib and a plurality of the belt-shaped reinforcing ribs
extended from the central reinforcing rib toward the peripheral
edge of the rear surface of the face part. Therefore the center of
the face part subjected to a highest degree of shock has an
enhanced rigidity. Further since the belt-shaped reinforcing ribs
are extended radially from the central reinforcing rib toward the
peripheral edge of the rear surface of the face part, the rigidity
of the face part can be prevented from being excessively increased,
and the stress acting on the face part can be uniformly
dispersed.
[0019] The maximum value of the Mises stress generated by the
collision between the golf ball model and the golf club head model
at the off-center positions of the front surface of the face part
thereof is set to less than 1.3 times the maximum value of the
Mises stress generated by the collision between the golf ball model
and the golf club head model at the center of the front surface of
the face part thereof. Therefore the restitution performance of the
golf club head model generated by the collision between the golf
ball model and the golf club head model at the off-center positions
of the front surface of the face part thereof is similar to that of
the golf club head model generated by the collision between the
golf ball model and the golf club head model at the center (sweet
area) of the front surface of the face part thereof.
[0020] The ratio of the maximum Mises stress generated at the
off-center position of the face part to that generated at the
center thereof is set to less than 1.3. But it is preferable to
approximate the above-described ratio to one. Thus it is preferable
to set the above-described ratio to not less than 1 and less than
1.3.
[0021] The golf club-designing method of the present invention is
carried out based on the stress value computed by using the finite
element method. Thus it is very easy to design the golf club head
without performing steps of making actual golf club heads on an
experimental basis or measuring the stress value. Further because
the computer is used, the configuration and material of the golf
club head can be changed by merely altering input data. Thus it is
easy to design the face part of the golf club head having various
patterns in an imaginary space by using the computer.
[0022] More specifically, the club head model is a wood club head
model. When the maximum value of the Mises stress generated when
the ball model collides with the golf club head model at the
off-center positions of the face part thereof is more than 1.3
times the maximum value of the Mises stress generated when the golf
ball collides with the golf club head model at the off-center
positions of the face part thereof, the sectional areas of the
reinforcing ribs, disposed on the rear surface of the face part,
which correspond to the collision positions, the width or/and the
height thereof are set large, whereas when the above-described
ratio is less than 1.0 time, the sectional areas of the reinforcing
ribs, disposed on the rear surface of the face part, which
correspond to the collision positions, the width or/and the height
thereof are set small.
[0023] The number of the belt-shaped reinforcing ribs formed on the
rear surface of the face part is set to not less than four nor more
than 10.
[0024] When the number of the belt-shaped reinforcing ribs is less
than four, the face part has a wide region where the belt-shaped
reinforcing ribs are not formed. Thus the region has an
insufficient strength. On the other hand, when the number of the
belt-shaped reinforcing ribs is more than 10, the face part has a
very high rigidity. Consequently the face part is excessively
restrained from vibrating and has a low restitution performance,
thus providing little reinforcing effect.
[0025] The Mises stress generated in each of the elements when the
ball model collides with the club head model is computed from a
main stress value at an integration point of each of the elements,
and the maximum value of the Mises stress at each of the collision
positions is computed from a change of the time series of the
determined Mises stress. The Mises stress can be computed by
analyses based on the finite element method (FEM). One value of the
Mises stress is obtained for one element. The value of the Mises
stress is optimum for determining whether the material of the face
part is destroyed.
[0026] When the ball model collides with the golf club head model
at an initial speed of 40 m/second, the maximum value of the Mises
stress generated in the face part is computed. The initial speed of
40 m/s is generated when an ordinary golfer hits a golf ball with a
wood golf club head. When the difference between the maximum values
of the Mises stress falls in the above-described range at the
initial speed of 40 m/second, it is possible to make the stresses
of the entire face part uniform and sufficiently hold the strength
of the face part when the golf ball is hit at other head
speeds.
[0027] The off-center collision positions, namely, positions other
than the center position of the front surface of the face part
means the region surrounding the geometrical center of the front
surface thereof. It is favorable that at least four positions
including positions upward and downward from the center position
and left-hand and right-hand positions thereof surrounding the
center position of the front surface of the face part are set as
the collision positions. It is more favorable that a portion of the
front surface of the face part corresponding to a portion of the
rear surface thereof where the reinforcing rib is formed and a
portion of the front surface thereof corresponding to a portion of
the rear surface thereof where the reinforcing rib is not formed,
which is sandwiched between the adjacent reinforcing ribs, are set
as collision positions.
[0028] As the number of the collision positions increases, it is
possible to design the golf club head with higher precision, but
the period of time required to perform computations increases. If
the off-center positions close to the center position are set as
the collision positions, stress values generated at the off-center
positions are almost equal to those generated at the center
positions by computations. Thus it is preferable that the
off-center collision positions are spaced at equal intervals from
the center position.
[0029] The designing method of the present invention is suitably
applied to the wood head having various configurations such as the
wood head having a hollow portion. The designing method of the
present invention is effective for designing the head of a driver
and the head of fairway wood clubs #1 through #9.
[0030] The designing method of the present invention which is
carried out by utilizing a computer is also applicable to designing
of an iron head to approximate the stress generated outside the
sweet area to that generated in the sweet area.
[0031] The designing method of the present invention forms a model
of the configuration of the face part of the golf club head by
using a computer. Thus the designing method is capable of forming
various configurations of the face part. For example, the face part
is allowed to have the shape of an approximately flat plate having
a flat surface or/and a curved surface. The face part can be made
of metal such as titanium and alloys of titanium or the like. The
material for a portion of the face part of the head model can be
altered from that of the other portion thereof. It is necessary to
input values indicating the properties of the material for the
portion of the face part to be altered.
[0032] The golf ball model can be made of materials that have been
hitherto used. Thus rubbers, polymer compositions containing
synthetic resin, and the like can be used to compose the golf ball
model.
[0033] The golf club head model can be composed of solid elements.
As the number of elements of the head model increases, computations
can be performed with higher accuracy. In consideration of design
efficiency, the number of the solid elements is preferably 60,000
to 200,000 when a tetrahedral solid element is used. The
above-described range is set in consideration of the ability of the
present-day computer. As the performance of the computer is
improved, the period of time required to perform computations
becomes shorter. Thus the head model can be composed of more
elements in the future. The deformed configuration of the golf club
head at a hitting time may be displayed from coordinate values of
nodal points of each element. Thereby the deformed configuration of
the golf club head at a ball hitting time can be evaluated, which
is effective for designing the golf club head.
[0034] In the present invention, it is preferable to use
tetrahedral secondary elements or hexagonal elements, when the size
of one side of each element cannot be made sufficiently small in
dividing the golf club head model and the golf ball model into
finite elements. When the size of one side of each element can be
made sufficiently small, tetrahedral primary elements may be
used.
[0035] When the tetrahedral elements are used, the angle of an edge
thereof is set to not less than 20 degrees nor more than 120
degrees.
[0036] It is preferable that the face part has not less than two
layers in the thickness direction thereof. When the tetrahedral
secondary elements are used, it is preferable that the length of
one side of each of the tetrahedral secondary elements is set to
not less than 1.0 mm nor more than 3.0 mm.
[0037] When the tetrahedral primary elements are used, it is
conceivable that the length of one side thereof is half of the
length of one side of the tetrahedral secondary element to improve
accuracy. But in consideration of a computing period of time, it is
preferable that the length of one side thereof is not less than 0.5
mm nor more than 1.25 mm.
[0038] The present invention provides the following three types of
golf club heads.
[0039] The golf club head of the first present invention is
designed by the first designing method.
[0040] The second golf club head is not limited to the first
designing method, but may be designed by other designing methods.
In the second golf club head, a central reinforcing rib is formed
at a central portion of a rear surface of a face part and not less
than four nor more than 10 belt-shaped reinforcing ribs are
extended radially from the central reinforcing rib toward a
peripheral edge of the rear surface of the face part. Values of
Mises stresses generated by collision between a golf ball and the
golf club head at off-center positions of a front surface of the
face part thereof is set to less than 1.3 times a value of a Mises
stress generated by collision between the golf ball and the golf
club head at a center of the front surface of the face part
thereof.
[0041] In the third golf club head, a central reinforcing rib is
formed at a central portion of a rear surface of a face part and
not less than four nor more than 10 belt-shaped reinforcing ribs
are extended radially from the central reinforcing rib toward a
peripheral edge of the rear surface of the face part. A ratio (W/t)
of a width W of each of the belt-shaped reinforcing ribs to a
thickness (height) t thereof is set to not less than 15 nor more
than 40. Each of the belt-shaped reinforcing ribs forms an
intersection angle of not less than 100 degrees nor more than 160
degrees with respect to a reference plane of the rear surface of
the face part.
[0042] In any of the above-described golf club heads, the central
portion of the rear surface of the face part is the region
surrounding the geometrical center of the rear surface of the face
part. A plurality of the belt-shaped reinforcing ribs is confluent
with each other in the central portion of the rear surface of the
face part. The central reinforcing rib is circular, elliptic or
polygonal in a sectional view. The configuration of the central
reinforcing rib is varied according to the extended direction and
the like of the belt-shaped reinforcing ribs. The sectional area of
the central reinforcing rib is also varied according to the values
of the Mises stresses.
[0043] The belt-shaped reinforcing ribs may be extended radially
from the central reinforcing rib to the peripheral edge of the rear
surface of the face part. But they do not have to be necessarily
extended to peripheral edge of the rear surface of the face part.
The belt-shaped reinforcing ribs are approximately linearly
extended in a predetermined width to the peripheral edge of the
rear surface of the face part. But they may be partly bent or
curved.
[0044] In the first and second golf club heads, the values of the
Mises stresses generated by the collision between the golf ball
model and the golf club head model at the positions other the
center position of the front surface of the face part are set to
less than 1.3 times the maximum value of the Mises stress generated
by the collision between the golf ball model and the golf club head
model at the center of the front surface of the face part
thereof.
[0045] In the third golf club head, as described above, not less
than four nor more than 10 belt-shaped reinforcing ribs are
extended radially from the central reinforcing rib toward the
peripheral edge of the rear surface of the face part. The ratio of
the width of each of the belt-shaped reinforcing ribs to the
thickness (height) thereof is set to the above-described specified
range. Further each of the belt-shaped reinforcing ribs forms the
above-described specified intersection angle with respect to the
reference plane of the rear surface of the face part. Similarly to
the first and second inventions, the values of the Mises stresses
generated by the collision between the golf ball model and the golf
club head model at the off-center positions of the front surface of
the face part thereof are set to less than 1.3 times the maximum
value of the Mises stress generated by the collision between the
golf ball model and the golf club head model at the center position
of the front surface of the face part thereof.
[0046] The reason the ratio (W/t) of the width W of each of the
belt-shaped reinforcing ribs to the height t thereof is set to not
less than 15 nor more than 40 is as follows: When the ratio of W/t
is less than 15, a high stress is generated at the boundary between
the reinforcing ribs and the rear surface of the face part and a
stress concentrates on the boundary. Thereby the stress cannot be
made uniform. On the other hand, if the ratio of W/t is more than
40, the reinforcing rib has an insufficient reinforcing effect.
[0047] The reason each of the belt-shaped reinforcing ribs forms
the intersection angle of not less than 100 degrees nor more than
160 degrees with respect to the reference plane of the rear surface
of the face part is as follows: If the intersection angle is less
than 100 degrees, a stress is generated at the boundary between the
belt-shaped reinforcing ribs and the rear surface of the face part.
Thereby there is a possibility that the face part cracks. On the
other hand, if the intersection angle is more than 160 degrees, the
belt-shaped reinforcing ribs provide an insufficient reinforcing
strength.
[0048] It is preferable that any of the first through third golf
club heads are wood heads. The face part is composed of a metal
plate. The reinforcing ribs are formed on the rear surface of the
metal plate.
[0049] It is preferable that the area of the central reinforcing
rib formed on the rear surface of the face part is set to not less
than 20% nor more than 90% of the area of the entire rear surface
of the face part.
[0050] When the area of the central reinforcing rib is out of the
above-described range, it is impossible to set the values of the
Mises stresses generated by the collision between the golf ball
model and the golf club head model at the off-center positions of
the front surface of the face part thereof to less than 1.3 times
the value of the Mises stress generated by the collision between
the golf ball model and the golf club head model at the center of
the front surface of the face part thereof.
[0051] It is preferable that in any of the first through third golf
club heads, the height, namely, the thickness (thickness of the
face part and that of reinforcing rib) obtained by the addition of
the thickness of the face part and that of the reinforcing rib is
uniform. It is preferable that the projected end surfaces of the
reinforcing ribs are on the same level.
[0052] Therefore the thickness of the reinforcing rib is set large
in a portion where the thickness of the face part is small, and the
thickness of the reinforcing rib is set small in a portion where
the thickness of the face part is large. Because the thickness of
the face part is large in the central portion thereof, the
thickness of the central reinforcing rib is small.
[0053] It is preferable that the thickness of the face part made of
the metal plate is set to not less than 0.5 mm nor more than 3.5
mm. When the thickness of the face part is less than 0.5 mm, the
face part has an insufficient strength. On the other hand, when the
thickness of the face part is more than 3.5 mm, the face part has a
very high rigidity and thus a low restitution performance.
[0054] It is favorable that the thickness of the central
reinforcing rib is not less than 2.6 mm nor more than 5.0 mm and
that the area of the central reinforcing rib is not less than 10
mm.sup.2 nor more than 1000 mm.sup.2.
[0055] When the thickness of the central region is less than 2.6
mm, the face part has an insufficient strength. On the other hand,
when the thickness of the central region is more than 5.0 mm, the
face part has a very high rigidity and thus a low restitution
performance. It is more favorable that the thickness of the central
region is not less than 2 mm nor more than 4 mm.
[0056] It is preferable that the sectional area of the belt-shaped
reinforcing rib is 2.0 mm.sup.2 to 10 mm.sup.2, that the width
thereof is 3 mm to 14 mm, and that the height thereof is 0.3 mm to
1.5 mm. When the sectional area of the belt-shaped reinforcing rib,
the width thereof, and the height thereof are less than 2.0
mm.sup.2, 3 mm, and 0.3 mm respectively, the face part has an
insufficient strength, and a stress concentration is liable to
occur. On the other hand, when the sectional area of the
belt-shaped reinforcing rib, the width thereof, and the height
thereof are more than 10 mm.sup.2, 14 mm, and 1.5 mm respectively,
the face part has a high rigidity and thus a low restitution
performance.
[0057] A portion where the adjacent belt-shaped reinforcing ribs
intersect with each other is rounded. The ratio (.theta./R) of an
intersection angle .theta. (degree) formed between the adjacent
belt-shaped reinforcing ribs to a radius of curvature R (mm) of the
rounded portion is set to favorably not less than three nor more
than 50 and more favorably not less than 6 nor more than 22.
[0058] When the ratio (.theta./R) is in the above-described range,
a stress does not concentrate on the rounded portion disposed at
the boundary between the adjacent belt-shaped reinforcing ribs, but
disperses. Thereby the face part has a high durability.
[0059] When the ratio of the intersection angle .theta. formed
between the adjacent belt-shaped reinforcing ribs to the radius of
curvature R is less than three, the radius of curvature R is large
with respect to the intersection angle .theta.. Thereby the thick
portion of the face part increases too much, which decreases the
coefficient of restitution thereof. On the other hand, when the
ratio (.theta./R) becomes large and exceeds 50, the radius of
curvature R is small with respect to the intersection angle
.theta.. Thereby a stress concentrates on the portion where the
adjacent belt-shaped reinforcing ribs intersect with each other and
thus the durability of the face part deteriorates.
[0060] As described above, according to the method of the present
invention for designing the golf club head carried out by using the
golf club head model and the golf ball model, simulation is
executed in an imaginary space by using a computer to set the
maximum value of the Mises stresses generated by the collision
between the golf ball model and the golf club head model at any
off-center positions of the front surface of the face part thereof
to less than 1.3 times the maximum value of the Mises stress
generated by the collision between the golf ball model and the golf
club head model at the center of the front surface of the face part
thereof. To do so, the positions of the reinforcing ribs and the
configurations thereof including the sectional areas and the
heights are changed. That is, the designing method of the present
invention allows the golf club head to be designed very easily
without performing steps of making actual golf club heads on an
experimental basis or measuring values of generated stresses.
Therefore the designing method of the present invention reduces the
expense and the period of time required to execute
computations.
[0061] In the golf club head formed based on the above-described
designing method and the second and third golf club heads, it is
possible to make stresses generated at any positions of the face
part thereof uniform. Further the stress generated by the collision
between the golf ball and the golf club head at the off-center
positions of the front surface of the face part thereof is
approximated to the stress generated by the collision between the
golf ball and the golf club head at the center of the front surface
of the face part thereof. Thereby the sweet area can be enlarged.
Therefore at the time ball-hitting at positions other than the
center of the face part (off-center shot), the golf club head has a
high strength and a superior restitution characteristic.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] FIG. 1 shows a flowchart showing the method of the present
invention of designing a golf club head.
[0063] FIG. 2A is a perspective view showing a golf club head
model.
[0064] FIG. 2B is a front view showing the golf club head
model.
[0065] FIG. 3 is a schematic view showing a golf ball model.
[0066] FIGS. 4A, 4B, and 4C are explanatory views showing a
situation in which the golf ball head model and the golf club head
model collide with each other.
[0067] FIG. 5 is a graph showing a change of a stress generated in
a certain element with the elapse of time when the golf club head
model hits the golf ball model.
[0068] FIG. 6 shows a golf club head according to an embodiment of
the present invention, in which FIG. 6A is a plan view showing a
rear surface of a face part; and FIG. 6B is a perspective view
showing the entire face part.
[0069] FIG. 7A is an explanatory view for explaining the definition
of an intersection angle .alpha. of a reinforcing rib with respect
to a reference plane of the rear surface of the face part.
[0070] FIG. 7B is an enlarged view showing a portion surround with
a rectangle of FIG. 7A.
[0071] FIG. 8A is an explanatory view for explaining the sectional
area of the reinforcing rib.
[0072] FIG. 8B shows the width and height of the reinforcing
rib.
[0073] FIG. 9 is an enlarged view showing a boundary portion
between adjacent belt-shaped reinforcing ribs adjacent to a central
reinforcing rib.
[0074] FIG. 10 is a plan view showing a rear surface of a face part
of an example 1.
[0075] FIG. 11 is a plan view showing a rear surface of a face part
of an example 2.
[0076] FIG. 12 is a plan view showing a rear surface of a face part
of an example 3.
[0077] FIG. 13 is a plan view showing a rear surface of a face part
of an example 4.
[0078] FIG. 14 shows an intersection angle of a reinforcing rib of
an example 5.
[0079] FIG. 15 shows an intersection angle of a reinforcing rib of
an example 6.
[0080] FIG. 16 is a plan view showing a rear surface of a face part
of an example 7.
[0081] FIG. 17 is a plan view showing a rear surface of a face part
of an example 8.
[0082] FIG. 18 shows an intersection angle of a reinforcing rib of
a comparison example 1.
[0083] FIG. 19 shows an intersection angle of a reinforcing rib of
a comparison example 2.
[0084] FIG. 20 is a plan view showing a rear surface of a face part
of a comparison example 3.
[0085] FIG. 21 is a plan view showing a rear surface of a face part
of a comparison example 4.
[0086] FIG. 22 is a graph showing results of analysis of a Mises
stress of the example 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0087] The embodiments of the present invention will be described
below with reference to drawings.
[0088] FIG. 1 is a flowchart showing the method of the present
invention of designing a golf club head. The designing method will
be schematically described below based on the flowchart.
[0089] Initially at step #1, from CAD data, a golf club head model
and a golf ball model to be analyzed by using a finite element
method (FEM) are prepared. That is, the wood golf club head model
and the golf ball model divided into finite elements are prepared.
In the golf club head model, a central reinforcing rib is formed at
the central portion of the rear surface of the face part, and a
plurality of belt-shaped reinforcing ribs is extended radially from
the central portion of the rear surface of the face part toward the
peripheral edge of the rear surface thereof. The positions of the
reinforcing ribs, the dimensions thereof such as widths and
heights, and the properties of a material of the face part are
specified.
[0090] At step #2, supposing that a golf ball collides with a golf
club head, simulation of hitting the golf ball model with the golf
club head model at the face center located at the geometrical
center of the face part of the golf club head model and at a
plurality of positions other than the face center is executed.
[0091] At step #3, computations are performed by using the finite
element method (FEM) to obtain a maximum value of Mises stresses
generated in finite elements of the front surface of the face part
of the club head model at each position of collision between the
golf ball model and the golf club head model.
[0092] At step #4, the difference in situations or values of
stresses generated on the face part according to hitting positions
is evaluated.
[0093] At step #5, when a maximum value of Mises stresses generated
by hitting the golf ball model with the golf club head model at
arbitrary positions of the front surface of the face part is less
than 1.3 times (less than 1.2 times preferably) a maximum value of
a Mises stress generated by hitting the golf ball model with
therewith at the center of the front surface of the face part, the
designing finishes and wood golf club heads are made on an
experimental basis and evaluated.
[0094] At step #6, if the situations or values of stresses
generated on the face part are out of the specified range,
simulation is executed again by changing the positions of the
reinforcing ribs and the configurations thereof including the
sectional areas and the heights in dependence on stress values.
Until the situations or values of generated stresses falls in an
allowable range, the positions of the reinforcing ribs and the
configurations thereof including the sectional areas and the
heights are controlled and hitting simulation are executed
repeatedly.
[0095] The designing method will be described in detail below.
[0096] Initially, golf club head model having the reinforcing ribs
formed on the rear surface of the face and the golf ball model are
prepared by using the computer, and an initial condition is
set.
[0097] FIGS. 2A and 2B show the wood golf club head model
(hereinafter referred to as merely head model) 1 used in the
simulation. The head model 1 is hollow. The face part 2 of the head
model 1 is plate-shaped and approximately elliptic. A plurality of
reinforcing ribs is formed at the central portion of the rear
surface of the face part 2 and in the region from the central
portion toward the peripheral edge of the rear surface thereof.
[0098] The head model 1 is divided into 64,247 tetrahedral primary
elements 1a, and a large number of nodal points 3 is obtained. The
average length of one side of each finite element is about 2.0 mm
in the face part and about 2.5 mm in the body part. The face part 2
is divided into 27,412 tetrahedral elements and has two layers.
Titanium is used as the material of the head model 1. As the
property of the material of the head model, the property of
titanium is inputted to the computer.
[0099] The head model 1 has a volume of 420 cc and weighs 191.0
g.
[0100] FIG. 3 shows a golf ball model (hereinafter referred to as
merely ball model) 5 used in the simulation. The ball model 5 is
made of an elastic material divided into solid elements each having
eight nodal points. The modulus of elasticity of the ball model 5
is so adjusted that the static compression characteristic thereof
is similar to that of a "HI-BRID everio" (manufactured by Sumitomo
Rubber Industries Inc.). The dimension and weight of the ball model
5 are also so adjusted that they are similar to those of the
"HI-BRID everio". The ball model 5 is divided into 11800 hexahedral
primary elements 5a, and a large number of nodal points 5b is
obtained. The length of one side of the finite element is 0.2 mm to
2 mm. As the property of the material of the ball model 5, the
modulus of elasticity and the Poisson's ratio are inputted to the
computer.
[0101] By using the head model 1 and the ball model 5, as shown in
FIGS. 4A, 4B, and 4C, simulation is conducted, supposing that a
golf ball is hit with a golf club head.
[0102] More specifically, after the ball model 5 is disposed near a
portion of the head model 1 at which the ball model 5 is hit with
the head model 1, the head model 1 collides with the ball model 5
at an initial speed of 40 m/second. A stress generated in each
element of the face part 2 of the head model 1 at the time of
collision is analyzed by using the finite element method (FEM).
[0103] FIG. 5 shows a situation in which a stress is generated in a
certain element at the time when the ball model 5 is hit with the
head model 1. As shown in FIG. 5, the value of generated stress
changes with the elapse of time (analysis step), the value of the
stress becomes maximum at about the middle point of the time period
of contact between the head model 1 and the ball model 5.
[0104] The stress is computed from the time of when the ball model
5 is hit with the head model 1 until the time when the ball model 5
separates completely from the head model 1. The coefficient of the
dynamic friction and that of the static friction at the time of the
contact therebetween are set to 0.3.
[0105] In this embodiment, the collision positions are set to a
face center position (CEN) and an off-center position on the
periphery of the center of the front surface 2a of the face part 2
with respect to a reference position, namely, the face center point
which is the geometrical center of the front surface 2a of the face
part 2. As the off-center collision position, the following eight
positions are set: a position at an interval of 10 mm upward from
the center position CEN, a position at an interval of 10 mm
downward from the center position CEN, a heel-side position spaced
at an interval of 20 mm from the center position CEN to the heel
side, a toe-side position spaced at an interval of 20 mm from the
center position CEN to the toe side, a heel-side obliquely upward
position spaced at an interval of 20 mm from the center position
CEN to the heel side and upward at an interval of 10 mm from the
center position CEN, a heel-side obliquely downward position spaced
at an interval of 20 mm from the center position CEN to the heel
side and downward at an interval of 10 mm from the center position
CEN, a toe-side obliquely upward position spaced at an interval of
20 mm from the center position CEN to the toe side and upward at an
interval of 10 mm from the center position CEN, and a toe-side
obliquely downward position spaced at an interval of 20 mm from the
center position CEN to the toe side and downward at an interval of
10 mm from the center position CEN.
[0106] Stresses generated in each element of the face part of the
head model 1 when the head model collides with the ball model at
the center position and the off-center positions are computed by
analyses based on the finite element method.
[0107] More specifically, an equation 1 shown below is used to
determine the Mises stress generated in each element of the face
part at each collision position based on a main stress value at an
integration point of each element of the face part. In the equation
1, .sigma.e is the Mises stress, .sigma.1 is a maximum main stress,
.sigma.2 is an intermediate main stress, and .sigma.3 is a minimum
main stress. .sigma. e = 1 2 .times. ( ( .sigma. 1 - .sigma. 2 ) 2
- ( .sigma. 2 - .sigma. 3 ) 2 - ( .sigma. 3 - .sigma. 1 ) 2 ) 1 2
Equation .times. .times. 1 ##EQU1##
[0108] A maximum value of the Mises stress generated in each
element is determined from a change in time series. The number of
integration points in the thickness direction thereof is set to
two. The maximum value of the Mises stress at all integration
points is determined. By carrying out this method, the maximum
value of the Mises stress generated in the face part is determined
at each of eight hitting positions.
[0109] When the maximum value of the Mises stress generated at the
off-center collision positions (positions on the periphery of the
face center) is not less than 1.3 times the maximum value of the
Mises stress generated at the face center collision position, the
conditions including the positions of the reinforcing ribs and the
configurations thereof including the sectional areas and the
heights are adjusted and hitting simulation are executed repeatedly
until the maximum value of the Mises stress generated at the
off-center positions becomes less than 1.3 times and preferably
less than 1.2 times the maximum value of the Mises stress generated
at the face center.
[0110] As an analysis software for simulation, an LS-DYNA
(manufactured by LSTC Inc.) is used. In addition, an ABAQUS
Explicit (manufactured by HKS Inc.) and a RAM-CRASH (manufactured
by ESI Inc.) can be used.
[0111] As the finite element model, a beam element, a shell
element, a solid element, and a combination of these elements can
be used. Analysis conditions can be altered appropriately.
[0112] The embodiment of the golf club head of the present
invention formed by using the above-described designing method is
described with reference to FIGS. 6 through 8.
[0113] The golf club head of the present invention may be formed by
using designing methods other than the above-described designing
method.
[0114] The wood golf club head 10 shown in FIGS. 6 through 9 has a
face part 12 for hitting a ball, a crown portion 13 extended from
the upper edge of the face part 12 to the rear upper edge of the
golf club head, a sole portion 14 extended from the lower edge of
the face part 12 to the rear lower edge of the golf club head, a
side portion 15 extended between the crown portion 13 and the sole
portion 14, and a hosel portion having a shaft hole (not shown) to
which a shaft (not shown) is bonded after the shaft is inserted
thereinto.
[0115] The golf club head 10 is made of metal such as a titanium
alloy. The golf club head 10 is composed of the face part 12 and a
body part 19 disposed rearward therefrom. The face part 12 and the
body part 19 are joined with each other at a boundary line K. The
face part 12 is formed by a forging method. The body part 19 is
formed by a lost wax precision casting method.
[0116] The material for the golf club head is not limited to a
titanium alloy, but it is possible to use one or more kinds of
metal materials including titanium, stainless steel alloy, aluminum
alloy, and magnesium alloy, and carbon fiber reinforced
plastic.
[0117] The face part 12 of the hollow golf club head 10 is composed
of a front surface portion 12a which contacts a ball when the ball
is hit with the golf club head 10 and a rear surface portion 12b
disposed rearward from front surface portion 12a, with a hollow
portion interposed therebetween. FIG. 6A is a rear view showing the
rear surface portion 12b of the face part 12. The hatched portion
in FIG. 6A shows a peripheral edge gs of the face part 12 that is
welded to the body part 19.
[0118] As shown in FIG. 6, a central reinforcing rib 70
approximately elliptic in a sectional view is formed at the central
portion of the rear surface of the face part 12. In addition,
belt-shaped reinforcing ribs 71 through 76 are extended radially
from the periphery of the central reinforcing rib 70 toward the
peripheral edge of the rear surface of the face part 12. In this
embodiment, six belt-shaped reinforcing ribs 71 through 76 are
formed, but not less than four nor more than 10 belt-shaped
reinforcing ribs may be provided. The belt-shaped reinforcing ribs
71 through 76 have the same sectional specification (sectional
area, sectional configuration, width, height) and are extended
substantially straight.
[0119] As shown in FIGS. 7A and 7B, each of the belt-shaped
reinforcing ribs 71 through 76 forms an intersection angle of
.alpha. to the reference plane of the rear surface of the face part
12. The intersection angle .alpha. is set to not less than 100
degrees nor more than 160 degrees to prevent a stress from
concentrating on a proximal portion of each of the belt-shaped
reinforcing ribs.
[0120] The intersection angle .alpha. is defined as follows:
[0121] As shown in FIG. 7A, in the section of the belt-shaped
reinforcing rib, a boundary point P3 between the belt-shaped
reinforcing rib having a width W and the rear surface of the face
part is set. At a position spaced by W/7 from the boundary point
P3, a line is drawn vertically to the rear surface of the face
part. As shown in FIG. 7B, the point at which the vertical line and
the front surface of the belt-shaped reinforcing rib intersect with
each other is denoted by P1. The point at which the vertical line
and the rear surface of the face part of the face part intersect
with each other is denoted by P2. The intersection angle .alpha. is
obtained by subtracting .angle.P1P3P2 from 180 degrees.
[0122] The sectional area of each of the belt-shaped reinforcing
ribs 71 through 76 is set to 2.0 mm.sup.2 to 10 mm.sup.2. The
sectional area of each of the belt-shaped reinforcing ribs 71
through 76 is set as follow: For example, with reference to FIG.
8A, a position spaced by 40% of a whole length L of the belt-shaped
reinforcing rib 72 from a center position 72c thereof in a
longitudinal direction thereof toward one end thereof is denoted by
72d. Similarly a position spaced by 40% of the whole length L of
the belt-shaped reinforcing rib 72 from the center position 72c
thereof in a longitudinal direction thereof toward the other end
thereof is denoted by 72e. The average of sectional areas of each
position in the longitudinal direction of the belt-shaped
reinforcing rib 72 in the range from the position 72d to the
position 72e is set as the sectional area of the belt-shaped
reinforcing rib 72.
[0123] As shown in FIG. 8B, the height t of each of the belt-shaped
reinforcing ribs 71 through 76 and the width W thereof are set to
0.3 to 2.0 mm and 8 to 22 mm respectively. The ratio (W/t) of the
width W to the height t is set to not less than 5.3 nor more than
74.
[0124] The height (thickness) of the central reinforcing rib 70 is
set to not less than 2.6 mm nor more than 5.0 mm. The sectional
area of the central reinforcing rib is set to not less than 10
mm.sup.2 nor more than 1000 mm.sup.2. That is, the sectional area
of the central reinforcing rib is set to not less than 20% nor more
than 90% of the area of the entire rear surface of the face part
12.
[0125] The intersection angle .theta. (.theta.1 to .theta.6) formed
between the adjacent belt-shaped reinforcing ribs 71 through 76 is
set to less than 90 degrees. At positions where the belt-shaped
reinforcing ribs 71 through 76 are continuous with the central
reinforcing rib 70, the adjacent belt-shaped reinforcing ribs
intersect with each other. A required radius of curvature R (R1 to
R6) is set at each of the positions where the adjacent belt-shaped
reinforcing ribs intersect with each other to allow the belt-shaped
reinforcing ribs 71 through 76 to be continuous with each other
smoothly.
[0126] The ratio (.theta./R) of the intersection angle .theta.
(degree) formed between the adjacent belt-shaped reinforcing ribs
71 through 76 to the radius of curvature R (mm) is set to not less
than three nor more than 50.
[0127] As shown in FIG. 9, the relationship between the radius of
curvature R and the intersection angle .theta. is as follows: at a
portion where a boundary line rk of the belt-shaped reinforcing rib
72 and a boundary line rk of the belt-shaped reinforcing rib 73
intersect with each other, as the ratio (.theta./R) of the
intersection angle .theta. formed between the belt-shaped
reinforcing ribs 72 and 73 to the radius of curvature R becomes
smaller, a radial line (m2) of the radius of curvature R becomes
increasingly far from the position rc where the center lines of the
belt-shaped reinforcing ribs 72 and 73 intersect with each other.
On the other hand, as the ratio (.theta./R) becomes larger, a
radial line (m1) of the radius of curvature R becomes increasingly
close to the position rc where the center lines of the belt-shaped
reinforcing ribs 72 and 73 intersect with each other.
[0128] When the ratio (.theta./R) becomes small and less than
three, the thick portion of the face part increases owing to an
increase of the area of the belt-shaped reinforcing rib. Thereby
the golf club head 10 has a low coefficient of restitution. On the
other hand, when the ratio (.theta./R) becomes large and exceeds
50, a stress concentrates on the portion where the adjacent
belt-shaped reinforcing ribs intersect with each other. Thus golf
club head has a low durability. Therefore the ratio (.theta./R) is
set to not less than 3 nor more than 50.
[0129] In the wood golf club head 10 having the above-described
construction, the positions, heights, widths, and sectional areas
of the reinforcing ribs 70 through 76 are set so that the maximum
value of the Mises stress generated at the off-center positions of
the front surface of the face part 12 is less than 1.3 times the
maximum value of the Mises stress generated at the center of the
front surface of the face part 12.
[0130] In the designing method of the present invention and the
golf club head designed by the designing method, it is possible to
secure the reinforcing effect provided by the reinforcing rib and
decrease the rigidity of the face part when the golf ball collides
with the face part at the off-center positions thereof. Thereby it
is possible to provide the golf club head with a high restitution
characteristic owing to improvement of the impedance matching and
enlarge the sweet area. Further the designing method allows the
golf club head to be designed very easily without performing steps
of making actual golf club heads on an experimental basis or
measuring the stress value. Moreover because the computer is used,
the configuration and material of the golf club head can be changed
by merely altering input data. Thus it is easy to design the face
part of the golf club head having various patterns in an imaginary
space by using the computer.
EXAMPLES
[0131] Golf club head models of the examples 1 through 8 shown in
table 1 and golf club head models of the comparison examples 1
through 4 shown in table 2 were formed by using a computer.
Simulation was executed by collision between ball models and the
golf club head models. The coefficient of restitution of each golf
club head model was determined to evaluate the performance of the
golf club head models.
[0132] Excluding the reinforcing ribs of the face part, the golf
club head models of all the examples and the comparison examples
were prepared by using the same specification. More specifically,
similarly to the embodiments shown in FIGS. 6 through 9, each of
the hollow golf club head models made of a titanium alloy was
formed by joining the face and body parts with each other to make
them approximately cup-shaped. The head had a volume of 405 cc. The
face part has an area of 4100 mm.sup.2. The thickness of the
portion of the face part where the reinforcing ribs were not formed
was set to 1.8 mm to 2.0 mm. TABLE-US-00001 TABLE 1 Unit E1 E2 E3
E4 E5 E6 E7 E8 Number of ribs 6 6 6 6 6 6 4 8 Drawing of rear
surface of face -- Height(t1)of section of rib mm 0.56 0.59 0.54
0.54 0.56 0.56 0.62 0.5 Width(W1) of rib mm 13 19 15 15 13 13 17 13
Height(t2)of section of rib mm 0.53 0.47 0.56 0.55 0.53 0.53 0.67
0.53 Width(W2) of rib mm 15 20 13 17 14 15 22 13 Height(t3)of
section of rib mm 0.53 0.49 0.56 0.55 0.53 0.53 0.62 0.53 Width(W3)
of rib mm 15 20 13 17 15 16 21 13 Height(t4)of section of rib mm
0.54 0.54 0.54 0.54 0.54 0.54 0.67 0.53 Width(W4) of rib mm 15 20
13 15 19 19 22 13 Height(t5)of section of rib mm 0.55 0.6 0.55 0.56
0.55 0.55 -- 0.55 Width(W5) of rib mm 15 20 16 13 19 19 -- 13
Height(t6)of section of rib mm 0.61 0.58 0.55 0.56 0.61 0.61 --
0.53 Width(W6) of rib mm 15 20 16 13 20 20 -- 13 Height(t7)of
section of rib mm -- -- -- -- -- -- -- 0.53 Wiclth(W7) of rib mm --
-- -- -- -- -- -- 13 Height(t8)of section of rib mm -- -- -- -- --
-- -- 0.53 Width(W8)of rib mm -- -- -- -- -- -- -- 13 Intersection
angle(.alpha.1) deg. 176 176 176 176 122 145 176 176 Intersection
angle(.alpha.2) deg. 176 176 176 176 122 145 176 176 Intersection
angle(.alpha.3) deg. 176 176 176 176 122 145 176 176 Intersection
angle(.alpha.4) deg. 176 176 176 176 122 145 176 176 Intersection
angle(.alpha.5) deg. 176 176 176 176 122 145 176 176 Intersection
angle(.alpha.6) deg. 176 176 176 176 122 145 -- 176 Intersection
angle(.alpha.7) deg. -- -- -- -- -- -- -- 176 Intersection
angle(.alpha.8) deg. -- -- -- -- -- -- -- 176 R1 mm 10 10 10 10 10
10 10 7 R2 mm 3 3 3 3 3 3 10 4 R3 mm 7 7 7 7 7 7 10 4 R4 mm 4 4 4 4
4 4 10 10 R5 mm 3 3 3 3 3 3 -- 7 R6 mm 10 10 10 10 10 10 -- 4 R7 mm
-- -- -- -- -- -- -- 4 R8 mm -- -- -- -- -- -- -- 10 .theta.1 deg.
65 65 65 65 65 65 90 45 .theta.2 deg. 40 40 40 40 40 40 90 45
.theta.3 deg. 75 75 75 75 75 75 90 45 .theta.4 deg. 65 65 65 65 65
65 90 45 .theta.5 deg. 40 40 40 40 40 40 -- 45 .theta.6 deg. 75 75
75 75 75 75 -- 45 .theta.7 deg. -- -- -- -- -- -- -- 45 .theta.8
deg. -- -- -- -- -- -- -- 45 Smax'/Smax -- 1.25 1.23 1.24 1.24 1.25
1.25 1.25 1.25 Thickness(H) of face center mm 2.8 2.8 2.8 2.8 2.8
2.8 2.8 2.8 Area of thickness portion mm.sup.2 78.5 113 80.1 78.2
78.2 78.2 78.2 78.2 Durability -- .circleincircle. .circleincircle.
.circleincircle. .circleincircle. .circleincircle. .largecircle.
.largecircle. .largecircle. where E denotes example.
[0133] TABLE-US-00002 TABLE 2 Unit CE1 CE2 CE3 CE4 Number of ribs 6
6 6 6 Drawing of rear surface -- of face Height(t1)of section of
rib mm 1.6 1 0.29 0.6 Width(W1) of rib mm 7 2.4 14 14 Height(t2)of
section of rib mm 1.6 1 0.29 0.6 Width(W2) of rib mm 4 2.4 14 14
Height(t3)of section of rib mm 1.6 1 0.29 0.6 Width(W3) of rib mm 7
2.4 14 14 Height(t4)of section of rib mm 1.6 1 0.29 0.6 Width(W4)
of rib mm 7 2.4 14 14 Height(t5)of section of rib mm 1.6 1 0.29 0.6
Width(W5) of rib mm 7 2.4 14 14 Height(t6)of section of rib mm 1.6
1 0.29 0.6 Width(W6) of rib mm 7 2.4 14 14 Intersection
angle(.alpha.1) deg. 110 90 176 176 Intersection angle(.alpha.2)
deg. 110 90 176 176 Intersection angle(.alpha.3) deg. 110 90 176
176 Intersection angle(.alpha.4) deg. 110 90 176 176 Intersection
angle(.alpha.5) deg. 110 90 176 176 Intersection angle(.alpha.6)
deg. 110 90 176 176 R1 mm 6 6 6 6 R2 mm 6 6 6 6 R3 mm 6 6 6 6 R4 mm
6 6 6 6 R5 mm 6 6 6 6 R6 mm 6 6 6 6 .theta.1 deg. 65 65 65 65
.theta.2 deg. 40 40 40 40 .theta.3 deg. 75 75 75 75 .theta.4 deg.
65 65 65 65 .theta.5 deg. 40 40 40 40 .theta.6 deg. 75 75 75 75
Smax'/Smax -- 1.32 1.35 1.32 1.32 Thickness(H) of face center mm
2.8 2.8 2.8 2.8 Area of thickness portion mm.sup.2 78.5 75 78.5
78.5 Durability -- .DELTA. X .DELTA. .DELTA. where CE denotes
comparison example.
[0134] In the tables 1 and 2, Smax denotes the maximum value of the
Mises stress generated at the center of face part, and Smax'
denotes the maximum value of the Mises stresses generated at
positions (off-center position) other than center of the face
part.
[0135] In the tables 1 and 2, to evaluate durability of the face
part of the golf club head of each of the examples 1 through 8 and
the comparison examples 1 through 4, a shaft and a grip were
mounted on each of the golf club heads to prepare golf clubs. By
using a swing robot, 1000 golf balls were hit with each golf club
at the center of the face part at a head speed of 50 m/second. The
durability of the golf clubs were marked by .largecircle., .DELTA.,
and X. The golf club in which the depth of a concave formed by
hitting was less than 0.1 mm was marked by .largecircle.. The golf
club in which the depth of a concave formed by hitting was not less
than 0.1 mm was marked by .DELTA.. The golf club whose face part
was destroyed before not more than 1,000 balls were hit thereby was
marked by X.
[0136] As shown in tables 1 and 2, the configuration of the rear
surface of the face part of each of the examples 1, 2, 3, and 4 is
shown in FIGS. 10, 11, 12, and 13 respectively. The entire
construction of the rear surface of the face part of each of the
examples 5 and 6 is the same as that of example 4. The intersection
angle of the belt-shaped reinforcing rib of each of the examples 5
and 6 with respect to the reference plane of the rear surface of
the face part is as shown in FIGS. 14 and 15 respectively. The
construction of the rear surface of the face part of each of the
examples 7 and 8 is shown in FIGS. 16 and 17 respectively.
[0137] The configuration of the golf club head of each of the
comparison examples 1 and 2 is as shown in FIG. 2A. The reinforcing
ribs of the comparison examples 1 and 2 formed 110.degree. and
90.degree. respectively to the reference plane of the rear surface
of the face part. The configuration of the face part of each of the
comparison example 3 and the comparison example 4 is as shown in
FIGS. 20 and 21 respectively.
[0138] The head model of each of the examples 1 through 8 and the
comparison examples 1 through 4 was prepared as shown in FIG. 2. In
addition ball models were prepared. The ball models collided with
the head models to analyze the Mises stresses generated at the
collision positions.
[0139] FIG. 22 shows the results of analyzed stress generated by
the head model of the example 1.
[0140] As the collision positions, the following eight positions
are set: a center position CEN (a), a U10 position (b) upward at an
interval of 10 mm from the center position CEN, a D10 position (c)
downward at an interval of 10 mm from the center position CEN, a
heel-side H20 position (d) spaced at an interval of 20 mm from the
center position CEN to the heel side, a toe-side T20 position (e)
spaced at an interval of 20 mm from the center position CEN to the
toe side, a heel-side obliquely upward H20U10 position (f) spaced
at an interval of 20 mm from the center position CEN to the heel
side and upward at an interval of 10 mm from the center position
CEN, a heel-side obliquely downward H20D10 position (g) spaced at
20 mm from the center position CEN to the heel side and downward at
an interval of 10 mm from the center position CEN, a toe-side
obliquely upward T20U10 position (h) spaced at an interval of 20 mm
from the center position CEN to the toe side and upward at an
interval of 10 mm from the center position CEN, and a toe-side
obliquely downward T20d10 position (i) spaced at an interval of 20
mm from the center position CEN to the toe side and downward at an
interval of 10 mm from the center position CEN.
[0141] In the head models of the examples 1 through 8 shown in
table 1, Smax'/Smax were less than 1.3. Thus it could be confirmed
that the restitution performance at the off-center positions of the
face part was similar to that at the center (sweet area) of the
face part. That is, it could be also confirmed that the sweet area
could be enlarged. The durability of the head models of the
examples 1 through 8 was favorably evaluated as .circleincircle.
and .largecircle..
[0142] On the other hand, in the head models of the comparison
examples 1 through 4 shown in table 2, Smax'/Smax exceeded 1.3.
Thus it could be confirmed that the restitution performance at the
off-center positions of the face part was different from that at
the center (sweet area) of the face part. That is, the restitution
performance obtained at the center position could not be obtained
at the off-center positions. The durability of the head models of
the comparison examples 1 through 4 was evaluated as .DELTA. or
X.
* * * * *