U.S. patent application number 09/332137 was filed with the patent office on 2002-02-21 for method of measuring rotational motion of a golf ball.
Invention is credited to KATAYAMA, SHU.
Application Number | 20020022531 09/332137 |
Document ID | / |
Family ID | 16158160 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020022531 |
Kind Code |
A1 |
KATAYAMA, SHU |
February 21, 2002 |
METHOD OF MEASURING ROTATIONAL MOTION OF A GOLF BALL
Abstract
A method of measuring rotational motion of a golf ball. A hit
golf ball is photographed by use of two cameras disposed along the
traveling direction of the golf ball with a predetermined distance
therebetween, and rotational motion of the golf ball is measured
based on the photographed images of the golf ball. There is used a
golf ball that has a no-depression polygonal mark in black or a
dark color close to black printed on the surface of the golf ball.
The hit golf ball is photographed by use of two cameras, and the
position of an angular point of the no-depression polygonal mark is
detected from photographed images, by means of image processing.
The rotational motion of the hit golf ball is calculated based on
change in position of the angular point in images photographed by
the two cameras.
Inventors: |
KATAYAMA, SHU; (SAITAMA,
JP) |
Correspondence
Address: |
SUGHRUE MION ZINN MACPEAK & SEAS
2100 PENNSYLVANIA AVENUE N W
WASHINGTON
DC
200373202
|
Family ID: |
16158160 |
Appl. No.: |
09/332137 |
Filed: |
June 14, 1999 |
Current U.S.
Class: |
473/151 ;
473/152; 473/156; 473/198 |
Current CPC
Class: |
A63B 24/0021 20130101;
A63B 2024/0031 20130101; A63B 2220/35 20130101; A63B 69/3658
20130101; A63B 2024/0034 20130101 |
Class at
Publication: |
473/151 ;
473/152; 473/156; 473/198 |
International
Class: |
A63B 069/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 1998 |
JP |
10-184718 |
Claims
What is claimed is:
1. A method of measuring rotational motion of a golf ball in which
a hit golf ball is photographed by use of two cameras disposed
along the traveling direction of the golf ball with a predetermined
distance therebetween, and the rotational motion of the golf ball
is measured based on the photographed images of the golf ball, said
method comprising the steps of: providing a golf ball having a
no-depression polygonal mark in black or a dark color close to
black printed on the surface of the golf ball; hitting a golf ball;
photographing the hit golf ball by use of two cameras; detecting
the position of an angular point of the no-depression polygonal
mark from photographed images, by means of image processing; and
calculating the rotational motion of the hit golf ball based on
change in position of the angular point in images photographed by
the two cameras.
2. A method of measuring rotational motion of a golf ball according
to claim 1, wherein said no-depression polygonal mark is an
isosceles triangle mark.
3. A method according to claim 2, wherein the ratio between the
length of the base and the altitude of the isosceles triangle is
within the range of 1:1 to 1:3.
4. A method according to claim 2, wherein the length of the base of
the isosceles triangle is 6-15 mm.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of measuring
rotational motion of a golf ball that moves at an ultrahigh speed,
in which method the golf ball is photographed in order to analyze
the motion of the golf ball.
[0003] 2. Description of the Related Art
[0004] Conventionally, DINAFAX (trade name) is available on the
market as an apparatus for photographing a golf ball in a state in
which the golf ball moves at an ultrahigh speed, such as an impact
state in which the golf ball receives an impact from a swinging
golf club. The DINAFAX has a rotatable cylindrical unit, and a film
is disposed on the inner circumferential surface of the cylindrical
unit. A lens is provided at a position located away from the center
of the cylindrical unit along the axial direction thereof. An image
obtained through the lens is projected onto the film through a
prism. For high speed photography, the cylindrical unit rotates to
thereby sequentially photograph images on the film. Also, Japanese
Patent Application Laid-Open (kokai) No. 62-104279 discloses a
method which uses a high-speed instantaneous multi-image recording
apparatus in combination with a video camera and a strobe.
[0005] However, the former method involves the process of
developing a film and a problem that when the motion of an object
to be photographed continuously varies at an ultrahigh speed,
whether or not the object has been successfully photographed is
unknown until development is completed. Accordingly,
re-photographing is often required, in turn requiring much labor
and time for experimentation. According to the latter method, the
strobe flashes repeatedly to photograph a number of images of a
dynamic object within one display area (multi-image photography)
while the shutter of the video camera is open. Thus, this method
can be carried out only in a dark place (in a place having at most
the brightness of a room). Also, the apparatus itself is very
expensive.
SUMMARY OF THE INVENTION
[0006] The present invention has been accomplished in view of the
above problems, and an object of the present invention is to
provide a method of measuring rotational motion of a golf ball
capable of being carried out both outdoors and indoors through use
of a relatively inexpensive apparatus.
[0007] To achieve the object, the present invention provides a
method of measuring rotational motion of a golf ball in which a hit
golf ball is photographed by use of two cameras disposed along the
traveling direction of the golf ball with a predetermined distance
therebetween, and the rotational motion of the golf ball is
measured based on the photographed images of the golf ball. The
method comprises the steps of: providing a golf ball having a
no-depression polygonal mark in black or a dark color close to
black printed on the surface of the golf ball; hitting the golf
ball; photographing the hit golf ball by use of two cameras;
detecting the position of an angular point of the no-depression
polygonal mark from photographed images, by means of image
processing (specifically, automatic image processing performed by
use of a computer); and calculating rotational motion of the hit
golf ball based on change in position of the angular point in
images photographed by the two cameras.
[0008] As described above, the method of measuring rotational
motion of a golf ball according to the present invention enables
automatic measurement which can be carried out both outdoors and
indoors through use of a relatively inexpensive apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic view showing an apparatus which
employs a method according to the present invention;
[0010] FIG. 2 is a view showing an arrangement of components of the
apparatus shown in FIG. 1;
[0011] FIG. 3 is a time chart showing an operation of the apparatus
shown in FIG. 1; and
[0012] FIG. 4 is a view showing a monitor screen.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] An embodiment of the present invention will now be described
with reference to the drawings. FIG. 1 shows an example of an
apparatus employing the method of the present invention. The
apparatus includes golf ball setting means 12 for setting a golf
ball 11 in place; specifically, a tee for placing the golf ball 11
thereon, (hereinafter referred to as a tee 12); sensor means 13 for
detecting the passing (downswing) of a club head (not shown) for
hitting the ball 11; a first camera 14; a second camera 15; and a
control unit 16. The sensor means 13 is located behind the tee 12
with respect to the travel direction of the ball 11. The first
camera 14 and the second camera 15 are disposed ahead of the tee 12
with respect to the travel direction of the ball 11 such that they
are located a predetermined distance from the tee 12, are separated
from each other, and are aimed horizontally. The control unit 16
has trigger means for sending shutter signals to the respective
first and second cameras 14 and 15. When a detection signal is
received from the sensor means 13, the trigger means sends shutter
signals to the first and second cameras 14 and 15 at a proper
timing such that an appropriate time lag is provided between the
shutter signals sent to the first and second cameras 14 and 15.
Symbol M denotes a mark printed on the surface of the golf ball 11.
Before the performance of measurement according to the method of
the present invention, the golf ball 11 is set on the tee 12 such
that the mark M faces the cameras 14 and 15. The first and second
cameras 14 and 15 are preferably CCD cameras having a shutter speed
of {fraction (1/10,000)} to {fraction (1/200,000)} second.
[0014] The sensor means 13 includes a pair of optical sensors, or a
first sensor 13A and a second sensor 13B with a distance m1 of 70
mm therebetween (see FIG. 2), each composed of a light-emitting
element and a light-receiving element. The distance m2 between the
tee 12 and the sensor means 13 is preferably approximately 40 mm.
The distance m3 between the tee 12 and the first camera 14
preferably ranges from 50 to 300 mm, and the distance m4 between
the first and second cameras 14 and 15 preferably ranges from 100
to 250 mm. The positional height of the first and second cameras 14
and 15 with respect to the golf ball 11 (placed on the tee 12) must
be determined in consideration of the trajectory of the hit ball
11. According to the specific site where measurement is to be
performed, a light 17 may be provided for illuminating the
trajectory of the hit ball 11. Also, each of the cameras 14 and 15
may be equipped with a strobe 18 (flashing means) which operates
synchronously with the shutter of the camera. The horizontal
distance between the trajectory of the hit ball 11 and each of the
first and second cameras 14 and 15 is preferably 200 to 600 mm.
[0015] The control unit 16, which is connected to the sensor means
13 and the cameras 14 and 15 each equipped with the strobe 18
(specific connections are not illustrated), includes the
following:
[0016] (1) Control box
[0017] The control box includes the following:
[0018] a) Frame memory for recording photographed images
[0019] b) Image analysis unit
[0020] c) Timing control unit
[0021] Sensor control, shutter control, I/O (input/output)
[0022] d) CPU unit
[0023] e) FDD (floppy disk drive) and HDD (hard disk drive) or
flash memory
[0024] (2) Software
[0025] Software for performing the following functions:
[0026] a) Calculation and display of head speed, speed of a hit
ball, backspin, side spin, and launch angle (upward angle with
respect to a horizontal line and sideward angle with respect to a
reference line)
[0027] b) Calculation of trajectory and travel distance
[0028] c) Display of the following screens
[0029] screen divided into some display areas (2 display areas for
displaying the image of a ball and 1 display area for displaying
measured values)
[0030] Launch angle distribution screen
[0031] Carry and/or total distance distribution screen
[0032] Trajectory screen
[0033] d) Accumulation of data
[0034] (3) Monitor and printer
[0035] Next, the method will be described with reference to FIGS. 2
and 3. When the first and second sensors 13A and 13B detect the
passing of a golf club head, the control unit 16 calculates time t1
required for the club head to pass between the sensors. Based on
the measured time t1 and the distance between the sensors 13A and
13B, the control unit 16 calculates a head speed. Upon reception of
a detection signal from the second sensor 13B, the control unit 16
outputs a trigger signal to each of the cameras 14 and 15 and to
each of the strobes 18. In the present embodiment, a plurality of
head speeds is previously measured. During operation, a delay time
t2 and shutter intervals t3 are previously set in accordance with
an applicable head speed selected from the previously measured head
speeds.
[0036] FIG. 4 shows the monitor screen of the control unit 16 on
which images of the hit ball 11 are displayed. The monitor screen
40 is divided into four display areas. A first display area 40A
displays the side view of the hit ball 11 as obtained through the
first camera 14. A second display area 40B displays the side view
of the hit ball 11 as obtained through the second camera 15. A
third display area 40C displays measured values.
[0037] In the present invention, the shape of the mark M printed on
the golf ball 11 is a no-depression polygon. The term
"no-depression polygon" refers to a polygon in which none of the
sides passes through the interior of the polygon, when the side is
extended. In the present invention, the no-depression polygon is
preferably an isosceles triangle. The mark M is painted in black or
any dark color close to black in order to make it contrast well
with the color of the surface of the golf ball.
[0038] If the shape of the mark is an isosceles triangle, the ratio
between the length of the base and the altitude is within the range
of 1:1 to 1:3, more preferably around 1:1.5. If the ratio of the
altitude to the length of the base is so small that the shape of
the mark is close to an equilateral triangle, the three angular
points of the triangle become difficult to distinguish from one
another. In contrast, if the ratio of the altitude to the length of
the base is excessively large, the length of the base becomes small
relative to the diameter of the golf ball, resulting in difficulty
in image processing. The length of the base is preferably 6-15 mm,
more preferably about 10 mm. If the length of the base is less than
6 mm, image processing becomes difficult due to dimples formed on
the surface of the golf ball (that is, processing an image formed
on dimples becomes difficult). If the length of the base exceeds 15
mm, the altitude increases accordingly, resulting in an excessively
large mark. In this case, if the amount of side spin is large in a
hit ball, a portion of the mark easily becomes invisible to the
cameras.
[0039] In the present embodiment, the golf ball 11 is displayed in
white against a black background, and the profile of the golf ball
11 is extracted from each of the images displayed on the first and
second display areas 40A and 40B (FIG. 4), through use of a
digitization (white/black) technique. Next, the mark M is extracted
from an area inside the profile of the golf ball 11 through use of
a similar digitization technique. In some cases, a dimpled portion
inside the mark M is displayed in white due to the reflection of
light. In such cases, image processing (blackening) is performed so
as to blacken such a whitened portion.
[0040] After completion of the above-described procedure, the main
axis (the median joining the midpoint of the base and the vertex)
of the mark M is obtained. From this main axis, searching is
performed outwardly along directions perpendicular to the main axis
in order to detect a point where the color changes from black to
white. This searching procedure is performed along the main axis.
As a result, there are obtained two straight lines each passing
through the thus-searched locus of the color-change points, i.e.,
two legs of the triangular mark. Next, straight lines are defined
outside the black mark such that the straight lines perpendicularly
intersect the center pints of the legs of the triangular mark. From
these straight lines, searching is performed toward the black mark
so as to detect the base of the triangular mark. The legs and base
are preferably obtained through curve approximation in
consideration of the curvature of the spherical surface of the golf
ball.
[0041] After identification of the triangle, i.e., the mark M
through image processing, the three angular points 50x, 50y, and
50z of the triangle are obtained based on the three sides. The
three-dimensional vector of each of the three angular points 50x,
50y, and 50z is obtained based on images appearing in the first and
second display areas 40A and 40B with the ball 11 taken as a unit
ball having a radius of 1. Based on the movement of the ball 11
from its position in the first display area 40A to that in the
second display area 40B, the vector of the rotational axis of the
ball 11 is obtained. Through vector analysis of the thus-obtained
three-dimensional vector(s) of the point(s) and the thus-obtained
vector of the rotational axis, the amount of rotation of the ball
11 is obtained. Based on the vector of the rotational axis and the
thus-obtained amount of rotation, the amounts of backspin and side
spin of the ball 11 can be obtained. Also, a difference in vertical
position of the golf ball 11 between the first display area 40A and
the second display area 40B (FIGS. 4) is measured. Then, based on
the thus-measured difference in vertical position and the distance
m4 (horizontal distance), the upward launch angle of the ball 11
can be obtained.
[0042] Through use of CCD cameras having a shutter speed of
{fraction (1/10,000)} to {fraction (1/200,000)} as the cameras 14
and 15 in combination with respective strobes which operate
synchronously with the cameras, an image of a white golf ball is
displayed in the black background regardless of whether the method
of the present invention is carried out indoors or outdoors. Also,
a no-depression polygonal mark printed on a ball is also clearly
displayed in black. The movement of a certain point(s) on the mark
appearing on a golf ball image is automatically obtained on a
computer through use of an image-analyzing technique such as a
digitization technique to thereby calculate the amount of spin of a
golf ball. Likewise, through the computer image analysis using a
digitization technique or the like, the launch angle of a golf ball
can be calculated. Accordingly, rotational motion of a golf ball
can be analyzed efficiently and accurately.
[0043] As described above, the present embodiment carrying out the
method of the present invention comprising the steps of: detecting
by sensor means the passing of a club head to hit a ball set at a
predetermined position; sending a detection signal from the sensor
means to trigger means of a control unit; and in response to the
detection signal, sending shutter signals from the trigger means to
respective first and second cameras at a proper timing, while
providing an appropriate time lag between the shutter signals, so
as to photograph the hit golf ball through the first and second
cameras, the first and second cameras facing horizontally, apart
from each other, and away from the set position of the ball at a
predetermined distance. According to the present invention, in
order to calculate the carry of a hit ball and to simulate the
trajectory of a hit ball, only the velocity of the hit ball, the
angle of hit, and the amount of backspin are measured as initial
conditions by means of the horizontally facing first and second
cameras. Thus, this system for measuring rotational motion of a
golf ball can be realized in a relatively simple configuration and
at low cost. Also, the operation is simple. Further, the system
highly facilitates the improvement of the swinging form of a
golfer, the development of golf balls, and the evaluation of
performance of golf balls. For example, a certain kind of ball may
be tested through use of different kinds of golf clubs to thereby
evaluate the performance of the golf clubs.
* * * * *