Launch monitor system and a method for use thereof

TECHNICAL FIELD OF THE INVENTION

The present invention relates to sports objects, and more particularly relates to an improved launch monitor system for analyzing two sports objects in a single swing, and a method for the use thereof.

BACKGROUND OF THE INVENTION

Athletes, and particularly golfers, are interested in improving their game performance. One of the elements in golf performance in the through-the-air carry distance and the directional accuracy resulting from the golf drive. Golf ball manufacturers can predict the landing point of a driven golf ball with great accuracy if they are given values for ball velocity, flight direction and ball spin in the immediate post-launch time period. In addition, manufacturers can diagnose problems in the golfer's swing if they are given the velocity, direction and rotary motions of the golf club head in the immediate pre-launch time period.

There are known monitoring devices for determining the position of a plurality of points on a single moving object at two closely spaced points in time which can be used to provide the required data useable in making such performance predictions. These systems have drawbacks with at least portability and/or accuracy.

A need, however, exists for a launch monitor system for capturing club motion data and ball motion data in a single swing, where the system is portable, easy to use, accurate and for use outdoors.

SUMMARY OF THE INVENTION

Broadly, the present invention comprises a launch monitor system and a method for use thereof, which analyses two separate sports objects in one swing such as a golf club and a golf ball.

According to one embodiment of the present invention the launch monitor system for measuring data for a club and a ball moving in a predetermined field-of-view includes at least one club camera, at least one ball camera, and a computer. The club and ball cameras are pointed toward the predetermined field-of-view. The club camera is positioned in a first plane and the ball camera is position in a second plane spaced vertically from the first plane. Each club camera obtains at least two club images in the predetermined field-of-view. Each ball camera obtains at least two ball images in the predetermined field-of-view. The computer determines club motion data from the club images and ball motion data from the ball images.

In one embodiment, the system further includes at least two club cameras and at least two ball cameras. In another embodiment, the system further includes at least one strobe light associated with each of the club and ball cameras.

According to one aspect of the present invention, the club and ball motion data is at least two-dimensional and preferably three-dimensional.

According to another embodiment of the present invention, the system includes the club and ball cameras pointed toward the predetermined field-of-view and the computer. The club and ball cameras are located on the same side of the club and ball. The computer determines club motion data from the club images and ball motion data from the ball images.

According to one feature of the above embodiments, the club includes at least two contrasting areas thereon and the ball includes at least one contrasting area thereon, and the club images include at least all of the club contrasting areas and the ball images include at least all of the ball contrasting areas.

According to the method of the present invention, the method comprising the steps of a golfer swinging a club to impact a ball; obtaining at least two club images during the swing at two different times; obtaining at least two ball images at two different times during the swing; determining the club motion data from the club images; and determining the ball motion data from the ball images.

Preferably, the club images are obtained before the club impacts the ball and the ball images are obtained after the club impacts the ball.

In this method, the step of determining the club motion data includes determining at least one of the following: speed, acceleration, loft angle, attack angle, path angle, face angle, droop angle, loft spin, face spin, droop spin, and hit location. In this method, the step of determining the ball motion data includes determining at least one of the following: velocity, launch angle, backspin, side angle, side spin rifling spin, carry distance, direction, and carry and roll distance.

In the method, the images of the club can be obtained during a downswing, a back swing or both.

Preferably, the club and ball data obtained can be used for individual players or groups of players in club design based on swings, for fitting club specifications, and to optimize the biomechanics of a player or a group of players.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a perspective view of one embodiment of a launch monitor system of the present invention that includes a club monitor and a ball monitor;

FIG. 2

is an enlarged, side, perspective view of the launch monitor system of

FIG. 1

;

FIG. 3

is an enlarged, perspective view of the ball monitor of

FIG. 1

;

FIG. 4

is an enlarged, top view of the ball monitor of

FIG. 3

;

FIG. 5A

is an enlarged, perspective view of a club head before a club calibration fixture is attached;

FIG. 5B

is an enlarged, perspective view of a teed-up ball;

FIG. 6

is an enlarged, perspective view of the club head of

FIG. 5A

after the club calibration fixture is attached;

FIG. 7

is a front view of a club monitor fixture for use with the club monitor shown in

FIG. 1 and a

ball monitor fixture for use with the ball monitor shown in

FIG. 1

;

FIG. 8

is a flow chart describing the operation of the system;

FIG. 9

is a perspective view of a three-dimensional field of view of the club monitor showing the golf club moving partially there through and showing a measured position A, a measured position B, and a projected impact position C;

FIG. 10

is a perspective view of a three-dimensional field of view of the ball monitor showing a golf ball moving there through and showing a measured position D and a measured position E;

FIG. 11

is a front view of a monitor screen showing the image obtained by a first club camera of the club monitor;

FIG. 12

is a front view of the monitor screen showing the image obtained by a second club camera of the club monitor;

FIG. 13

is a front view of the monitor screen showing the image obtained by a first ball camera of the ball monitor;

FIG. 14

is a front view of the monitor screen showing the image obtained by a second ball camera of the ball monitor;

FIG. 15

is a flow chart describing the calibration of the club head; and

FIG. 16

is a flow chart describing the calibration of the club and ball monitors; and

FIG. 17

is a flow chart describing the determination of markers in images.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1

illustrates a preferred launch monitor system

10

of the invention. The launch monitor system

10

includes a support structure

12

, club monitor

14

, a ball monitor

16

, a microprocessor

18

, a computer

20

, and a monitor

22

. The microprocessor

18

and computer

20

are shown as separate units but may be combined into a single element. Similarly, the computer

20

and monitor

22

are shown as separate units but may be combined into a single element. The microprocessor

18

and computer

20

have several algorithms and programs used by the system to control the system and make the determinations, as discussed below.

Referring to

FIGS. 1 and 2

, the support structure

12

includes a rear frame

24

, a lower frame subassembly

26

, an upper frame assembly

28

, a lower base

30

, an upper base

32

, and a rod

34

. The rear frame

24

includes two parallel horizontal frame members

35

and

36

spaced apart and two parallel vertical frame members

38

and

40

(as shown in

FIG. 1

) spaced apart. These members

35

-

40

are fastened together to form a rectangle.

The lower frame subassembly

26

includes two frame members

42

and

44

connected to the vertical frame members

38

and

40

, respectively, with braces

46

and fasteners so that the members

42

and

44

extend substantially perpendicular to members

38

and

40

, respectively. The lower frame subassembly

26

further includes a member

48

that extends between the members

42

and

44

and is connected thereto with braces

50

and fasteners so that the member

48

is spaced vertically from the members

42

and

44

. The member

48

includes grooves

48

a

in its front and rear faces.

The upper frame subassembly

28

includes two parallel frame members

52

and

54

spaced apart and two parallel frame members

56

and

58

(as seen in

FIG. 1

) spaced apart. These members

52

-

58

are fastened together to form a rectangle. The members

56

and

58

are connected to vertical members

38

and

40

, respectively, with braces

60

, fixed fasteners, and relatable fasteners

62

. In this way, the upper frame subassembly

28

can rotate to change its angle α with a horizontal plane H. Plane H is parallel to the ground G. The members

52

and

54

have grooves

52

a

and

54

a

in the front and rear faces.

Additional braces, not discussed but shown, maybe used between the members of the frame so that the frame has the necessary structural rigidity. The frame may have a different configuration so long as it supports monitors

14

and

16

(as shown in

FIG. 1

) in the necessary orientation and provides the adjustability that the operator desires. Clamps can be connected to the bases

30

and

32

to retain the bases at a particular position. This frame can be formed of various materials, such as aluminum.

The rear end of the lower base

30

is connected to the member

48

of the frame via grooves

48

a

and a slide member

64

so that the base

30

is movable along the length of member

48

. The front end of the lower base

30

has pads (not shown) as best seen in

FIG. 3

for slidably cooperating with rod

34

. The rod

34

is formed in separable segments so that it can be disassembled and assembled, alternatively a single-piece rod can be used.

The upper base

32

includes support members

68

onto which rotatable wheels

70

are mounted. The support members

68

and the wheels

70

are configured and dimensioned to cooperate with the grooves

52

a

and

54

a

so that the base

32

moves along the length of the members

52

and

54

.

Referring again to

FIG. 1

, the club monitor

14

is disposed aligned with a first horizontal plane H

1

defined by the base

32

, the ball monitor

16

is disposed aligned with a second horizontal plane H

2

defined by the base

30

so that the club monitor

14

is vertically spaced there above by a distance ΔH. The monitors

14

and

16

are further preferably positioned so that the center C

1

of the club monitor

14

is spaced from the center C

2

of the ball monitor

16

by a distance ΔC. This arrangement allows the launch monitor system to capture images of a golf club

71

and a golf ball

72

, as shown in

FIGS. 5A and 9

, as discussed in detail below.

Referring to

FIG. 1

, the club monitor

14

includes a first club camera CC

1

, a spaced second club camera CC

2

, a control box

73

, four reflective elements

74

,

76

,

78

,

80

, a first club motion sensor

82

on a support

84

, a second club motion sensor

86

on a support

88

.

The cameras CC

1

and CC

2

used are electro-optical cameras with light-receiving apertures, shutters, and light sensitive silicon panels. CCD cameras are preferred but TV-type cameras are also useful. Recommended commercially available club cameras are manufactured by Sony under the name XC55⅓ inch diagonal CCD's.

Referring to

FIGS. 3 and 4

, video lines

89

from the respective cameras CC

1

, CC

2

lead to control box

73

. The control box

73

includes a strobe light unit

90

and an optical or Fresnel lens

92

in front of the strobe light unit. The strobe light unit

90

is comprised of a single flash bulb assembly, the related circuitry, and a cylindrical flash tube. The strobe light unit single flash bulb assembly is capable of flashing faster than every 1000 microseconds. The circuits used with the strobe light unit are the subject of commonly assigned U.S. Pat. No. 6,011,359 to Days, which is incorporated herein in its entirety by express reference thereto.

The reflective elements or panels

74

,

76

,

78

and

80

are mounted to base

32

. Reflective panels

74

,

76

also include respective apertures

94

,

96

and the cameras CC

1

and CC

2

and panels

74

,

76

are mounted such that lenses

98

,

100

(as shown in

FIG. 4

) are directed through the respective apertures

94

,

96

in the reflective panels

74

,

76

. Third and fourth reflective elements

78

and

80

are disposed in front of the Fresnel lense

92

. Panel

78

reflects about one-half of the light from flash bulb unit

90

into panel

74

, while panel

80

reflects the other half of the light into light-reflecting panel

76

. Alternatively, ring-shaped strobe lights can be used which surround each camera lens, which would eliminate the need for reflective panels all together. The panels can also be eliminated if single or dual strobe lights adjacent each camera are used such as disclosed in U.S. Pat. No. 5,575, 719 to Gobush et al. and incorporated herein in its entirety. Panels

74

,

76

,

78

and

80

may be plates formed of polished metal, such as aluminum, stainless steel, chrome-plated metal, or gold-plated metal.

Referring again to

FIG. 1

, club cameras CC

1

and CC

2

are electrically connected to the microprocessor

18

and computer

20

via cables

102

. The first club motion sensor

82

and the second club motion sensor

86

shown are photoelectric sensors manufactured by Tritronics. The sensors

82

and

86

are for use with a reflective mount

104

. The mount

104

includes a base

106

and two cylindrical rods

108

and

110

. The cylindrical rods

108

and

110

have strips of reflective material on the side facing the cameras CC

1

and CC

2

. A beam from the first club motion sensor

82

is reflected back to the sensor from the material on rod

108

. A beam from the second club motion sensor

84

is reflected back to the sensor from the material on rod

110

. Other types of sensors, such as a photodetector used with a receiving source, can also be used to actuate the monitor

14

cameras CC

1

and CC

2

.

The ball monitor

16

similar to the club monitor

14

includes a first ball camera BC

1

, a spaced second ball camera BC

2

, a control box

112

, four reflective elements

114

,

116

,

118

,

120

, a ball sensor

122

.

The cameras BC

1

and BC

2

used are electro-optical cameras with light-receiving apertures, shutters, and light sensitive silicone panels as discussed in U.S. Pat. No. 5,575,719. CCD cameras are preferred but TV-type cameras are also useful. Recommended commercially available ball cameras are manufactured by Electrim Corporation under the name EDC cameras.

The control box

112

and four reflective elements

114

,

116

,

118

,

120

are similar to those described with respect to the club monitor

14

.

The ball motion sensor

122

is a microphone and is used to initiate the operation of the monitor

16

. A laser or other apparatus (not shown) can also be used to initiate the system. For example, the initiating means can include a light beam and a sensor as with the club monitor

14

.

The ball cameras BC

1

and BC

2

are directly electrically connected to the microprocessor

18

and indirectly connected to the computer

20

. The microprocessor

18

tells the computer

20

to clear and ready the ball cameras. The sensor

122

is also electrically connected to the microprocessor

18

and the computer

20

.

Referring to

FIG. 5A

, the club

71

includes a club head

124

with a hosel

126

and a shaft

128

is attached to the hosel

126

. The club

71

further includes three (3) reflective spaced-apart round areas or markers

128

a-c

place thereon. The marker

128

a

is located on the toe of the club head

124

. The marker

128

b

is located on the free end of the hosel

126

. The marker

128

c

is located on the shaft

128

. Although three markers are preferred, as few as two can be used. The present invention is not limited to the number of markers disclosed herein. The location of the markers can be changed in ways known to those of ordinary skill in the art. For example, on one club head two markers can be placed on the toe and one on the hosel, or on another club head one marker can be placed on the toe and two markers can be placed on the hosel.

The markers

128

a-c

have diameters of one-fourth (¼) to one-eighth (⅛) of an inch are preferred but other size and shaped areas can be used. Markers

128

a-c

are preferably made of reflective material which is adhered to the club head

124

, hosel

126

, and shaft

128

. The “Scotchlite” brand beaded material made by Minnesota Mining and Manufacturing (3M) is preferred for forming the markers. Corner-reflective reflectors may also be used. Alternatively, painted markings, spots or a line can be used that defines at least one contrasting area.

The club head

124

further includes grooves

130

in the face. Groove

132

is disposed through the geometric center C of the club head and allows the geometric center C of the club head to be marked.

Referring to

FIG. 5B

, the teed ball

72

has similar markers

130

a-f

. The marker

130

f

is centrally located on the ball and the markers

130

a-e

are disposed thereabout. The angle between the non-central markers

130

a-e

is designated as β. It is recommended that the angle β is between about 10° and about 40°. Most preferably, the angle βis 30°. Rather than retro-reflective markers corner-reflective material or paint can also be used. Although six markers are shown, a single line or as few as two markers or as many as eleven markers can alternatively be used on the ball.

Referring to

FIG. 6

, in order to calibrate the club head

71

as discussed below, a club head calibration fixture

136

is used. The fixture

136

includes a magnetic base

138

which defines a centrally located bore

140

there through. Connected to the base

138

is an extension

142

. The extension has a face

144

that is aligned with a vertical orientation line v, and a notch

146

that allows the bore

140

in the base

138

to be visible. The face

144

includes retro-reflective markers

148

a-c

. Markers

148

a-b

are aligned with one another and marker

148

c

is offset from these markers.

Referring to

FIG. 7

, in order to calibrate the monitors

14

and

16

(shown in

FIG. 1

) as discussed below, a club monitor fixture

150

and a ball monitor fixture

151

are used. The club monitor fixture

150

includes a back wall

152

, a central wall or leg

154

extending from the back wall

152

, outer wall or legs

156

and

158

extend from the back wall

152

spaced from the central leg

154

. The length of the central leg

154

from the front surface of the back wall

152

is less than the length of the outer legs

156

and

158

from the front surface of the back wall

152

.

The calibration fixture

150

in use should be positioned within the field-of-view of the cameras CC

1

and CC

2

. Distance calibrators and tabs can be used with the fixture

150

to properly position it as disclosed in application Ser. No. 09/156,611 to Gobush et al. incorporated by reference in its entirety.

Calibration fixture

150

has a pattern of contrasting areas or retro-reflective markers

160

a-u

. Applicants have found that twenty-one markers are preferable. Fewer markers in the vertical direction on the calibration fixture are needed to adequately calibrate the system. The number of contrasting areas can be as low as six and more than twenty-one. Since the areas

160

a-u

are disposed on the back wall

152

, free end of the central leg

154

, and the free ends of the outer legs

156

and

158

, the markers are located in three dimensions. However, the markers can also be located only within two dimensions. The markers can be replaced with contrasting painted areas in two- or three-dimensions.

Fixture

150

can further include an optical level indicator and legs or spikes for leveling the fixture.

Ball fixture

151

is configured similarly to club fixture

150

however, since the ball monitor

16

(as shown in

FIG. 2

) views a scene closer to the ground than the club monitor

14

the ball fixture

151

is shorter than the club fixture

151

. Otherwise, the ball fixture

151

is configured similarly to the club fixture

150

and includes fifteen retro-reflective markers

162

a-o

. The number of contrasting areas can be as low as six and greater than fifteen. The modifications to the ball fixture can be similar to those suggested for the club fixture

151

.

The use of the system

10

(as shown in

FIG. 1

) is generally illustrated in FIG.

8

. At step S

101

, the system starts and determines if this is the first time the system has been used. By default, the system will use the last calibration when it is first activated. Therefore, the system must be calibrated each time the system is moved and/or turned on.

At step S

102

, the operator calibrates the club head and the system. After calibration, the system is set at step S

103

for either the left- or right-handed orientation, depending on the golfer to be tested. The selection of the left-handed orientation requires one set of coordinates are used for the left-handed golfer and right-handed system requires another set of coordinates for a right-handed golfer. At this time, the system is also set up as either a test or a demonstration. If the test mode is selected, the system will save the test data, while in the demonstration mode it will not save the data.

At step S

103

, additional data specific to the location of the test and the golfer is entered as well. Specifically, the operator enters data for ambient conditions such as temperature, humidity, wind speed and direction, elevation, and type of turf to be used in making the calculations for the golf ball flight, roll, and total distance. The operator also inputs the personal data of the golfer. This personal data includes name, age, handicap, gender, golf ball type (for use in trajectory calculations discussed below), and golf club used including information such as the type of club head (iron, driver, wood, loft, and lie) and information on the shaft.

After this data is entered, the system is ready for use and moves to step S

104

. At step S

104

, the system waits for the beam break between sensor

82

(as shown in

FIG. 1

) and rod

106

occurs when the club moves through the player's back swing. The sensor sends a signal to the microprecessor

18

to tell the computer to “arm” the ball cameras BC

1

and BC

2

so that they are ready to fire when signaled. Arming the ball cameras means the panel within the CCD camera is cleared and ready to be activated. The arming of the ball camera prior to taking images is due to the particular cameras BC

1

and BC

2

used. If other cameras are used that arm more quickly this step and the additional sensor

82

may not be necessary. The signal is also sent to the microprocessor

18

so that it is ready for the signal from the second swing sensor

86

.

On the downswing, the beam between sensor

86

and rod

108

causes the club monitor

14

to expose the sensor panels to light. When the beam from

86

is broken, the club monitor

14

strobes twice during the same exposure of the sensor panels so that two images of the club head

71

at position A and B (as shown in

FIG. 9

) are in a single frame. When a sound of a sufficient level is picked up by the microphone

122

, the ball monitor

16

(as shown in

FIG. 1

) obtains two images of the ball

72

(as shown in FIG.

10

). The amount of time between the club images in FIG.

9

and the ball images in

FIG. 10

is short, preferably 800 microseconds. The images are recorded by the silicon panel within each of the cameras, as discussed below and are used by the system to determine the club motion data and the ball motion data.

At steps S

105

-S

107

, the system uses several algorithms stored in the computer to determine the location of the golf ball relative to the monitor. After the computer has determined the location of the golf ball from the images, the system (and computer algorithms) determine the launch conditions. These determinations, which correspond to steps S

105

, S

106

, and S

107

, include locating the bright areas in the images, determining which of those bright areas correspond to the markers on the golf club or ball, and, then using this information to determine the location of the club or ball from the images, and calculate the data, as discussed below, respectively. Specifically, the system at step S

105

analyzes the images recorded by the cameras by locating the bright areas in the images. A bright area in the image corresponds to light from the flash bulb assembly reflecting off of the retro-reflective markers or markers on the golf club or ball.

Since the golf club preferably has three markers on it, the system should find six bright areas that represent the club markers in the images from each of the two cameras.

FIG. 11

represents the images received by camera CC

1

and

FIG. 12

represents the images received by camera CC

2

of the club head prior to ball impact as shown on monitor screen

22

a

. The system then determines which of those bright areas correspond to the golf club's reflective markers at step S

106

.

Since the ball preferably has 6 markers on it, the system should find twelve bright areas that represent the markers in the images from each of the cameras BC

1

and BC

2

(2 images of the golf ball with 6 markers).

FIG. 13

represents the images received by camera BC

1

and

FIG. 13

represents the images received by camera BC

2

of the ball after impact as shown on monitor screen

22

a

. The system then determines which of those bright areas correspond to the golf ball's reflective markers at step S

106

. As discussed in detail below, this can be done in several ways. If with the club only six markers are found in the image or with ball only twelve markers are found in the image, the system moves on to step S

107

to determine, from the markers in the images, the position and orientation of the golf ball during the first and second images.

However, if there are more or less than the desired number of markers or bright areas found in the images, then at step S

108

the system allows the operator to manually change the images. If too few bright areas are located, the operator adjusts the image brightness, and if too many are present, the operator may delete any additional bright areas. In some instances, the bright areas in the images may be reflections off of other parts of the golf ball or off the golf club head. If it is not possible to adequately adjust the brightness or eliminate those extraneous bright areas, then the system returns the operator to step S

104

to have the golfer hit another golf ball. If the manual editing of the areas is successful, however, then the system goes to step S

107

.

At step S

107

, the system uses the identification of the markers in step S

106

to determine the location of the centers of each of the six or twelve markers in each of the two images. Knowing the location of the center of each of the markers, the system can calculate the golf club's speed, loft angle, attack angle, path angle, face angle, droop angle, loft spin, face spin, droop spin, and hit location. In addition, the system can calculate the ball's velocity, launch angle, backspin, side angle, side spin rifling spin, carry distance, direction, carry and roll distance.

At step S

109

, the system uses this information, as well as the ambient conditions and the golf ball information entered at step S

103

to calculate the trajectory of the golf ball during the shot. The system will also estimate where the golf ball will land (carry), and even how far it will roll, giving a total distance for the shot. Because the system is calibrated in three dimensions, the system will also be able to calculate if the golf ball has been sliced or hooked, and how far off line the ball will be.

This information (i.e., the golfer's club and ball data) is then presented to the golfer at step S

110

, in numerical and/or graphical formats. At step S

111

, the system can also calculate the same information if a different golf ball had been used (e.g., a two-piece rather than a three-piece golf ball). It is also possible to determine what effect a variation in any of the launch conditions (golf ball speed, spin rate, and launch angle) would have on the results.

The golfer also has the option after step S

112

to take more shots by returning the system to step S

104

. If the player had chosen the test mode at step S

103

and several different shots were taken, at step S

113

the system calculates and presents the average of all data accumulated during the test. At step S

114

, the system presents the golfer with the ideal launch conditions for the player's specific capabilities, thereby allowing the player to make changes and maximize distance. The system allows the golfer to start a new test with a new golf club, for example, at step S

115

, or to end the session at S

116

.

Now turning to the calibration step S

102

(as shown in

FIG. 8

) which is represented in detail in

FIG. 15

, the calibration begins with calibrating the club head. Referring to

FIGS. 5A and 6

, as in step

201

the player selects a club head

71

. Then in step

202

, an operator using the center groove

132

locates and marks the geometric center C or sweet spot of the club head with a marking. With reference to

FIGS. 6 and 15

, in step S

203

the operator attaches the calibration fixture

136

to the club head face so that the geometric center C is centered in the bore

140

in the base

138

. As stated in steps S

204

and S

205

, the club head

71

is then set up in the field-of-view of the club monitor

14

and held stationary until a single image is obtained of the club head and fixture by the cameras CC

1

and CC

2

. The image will include contrasting areas due to reflection of the light from the monitor

14

off of markers

148

a-c

. The microprocessor

18

controls the timing of the cameras flashes. The transformation algorithm(s) in the computer

20

in step S

206

correlate points on the club head with respect to the reference point or geometric center of the club head. The details of the fixture

136

are disclosed in U.S. Pat. No. 5,575,719 to Gobush et al., incorporated by reference in its entirety.

With reference to

FIGS. 1 and 8

, calibration step S

102

after using the fixture

136

further includes calibrating the monitors

14

and

16

. The details of this step are illustrated in FIG.

16

. First, in step S

301

the system

10

is set up and leveled. The system

10

is preferably set up on level ground, such as a practice tee or on a level, large field. Obviously, it is also possible to perform the tests indoors, hitting into a net. The system is positioned to set the best view of the events and the predetermined fields-of-view. Then at step S

302

, the calibration fixtures

150

and

151

(as shown in

FIG. 7

) are placed in the appropriate locations within fields-of-view of monitor

14

and monitor

16

, respectively. This is about 40 inches from the fixture

150

to the CC

1

and CC

2

cameras and about 30 inches from the fixture

151

to the BC

1

and BC

2

cameras. Preferably, the calibration fixtures

150

and

151

are level and parallel to the system to ensure the best reflection of the light from the flash bulb assemblies in the monitors. Both cameras CC

1

and CC

2

and BC

1

and BC

2

of each monitor

14

and

16

, respectively, obtains a picture of each calibration fixture and send the image to a buffer in step S

303

.

In step S

304

, the system includes a calibration algorithm used to determine the location of the centers of the spots in each image corresponding to each calibration fixtures' retro-reflective markers

160

a-u

and

162

a-o.

The system must know the true spacing of the markers on the calibration fixture

150

. To make this determination for the club fixture

150

and monitor

14

, eleven constants determine the focal length, orientation and position of each camera CC

1

and CC

2

given the premeasured points on fixture

150

and the twenty-one U and V coordinates digitized on each camera's sensor panels.

Sensor panels of each camera CC

1

and CC

2

which receive successive light patterns that contain 480 lines of data and 640 pixels per line. A computer algorithm is used for centroid detection of each marker

160

a-u

. Centroid detection of a marker is the location of the center area of the marker for greater accuracy and resolution. Each image received from markers

160

a-u

results in an apparent x and y center position of each marker. Where light is low in the field of vision due to gating, an image intensifier may be used in conjunction with the sensor panels. An image intensifier is a device which produces an output image brighter than the input image.

The X, Y and Z coordinates of the center of each marker

160

a-u

which are arranged in a three-dimensional pattern were premeasured to accuracy of one of one-ten thousandth of an inch on a digitizing table and stored in the computer. An image of the calibration fixture

150

is obtained by the two cameras CC

1

and CC

2

.

This image determines the eleven (11) constants relating image space coordinates U and V to the known twenty-one X, Y and Z positions on the calibration fixture

150

. The equations relating the calibrated X(i), Y(i), Z(i) spaced points with the U

i

(j)

, V

i

(j)

image points are:

\begin{matrix} U_{i}^{j} = \frac{D_{1 j} X (i) + D_{2 j} Y (i) + D_{3 j} Z (i) + D_{4 j}}{D_{9 j} X (i) + D_{10 j} Y (i) + D_{11 j} Z (i) + 1} & (Eq . 1) \end{matrix}

where i=1,21; j=1,2.

\begin{matrix} V_{i}^{j} = \frac{D_{5 j} X (i) + D_{6 j} Y (i) + D_{7 j} Z (i) + D_{8 j}}{D_{9 j} X (i) + D_{10 j} Y (i) + D_{11 j} Z (i) + 1} & (Eq . 2) \end{matrix}

The eleven constants, Di1 (i=1,11) for camera CC

1

and the eleven constants, Di2 (i=1,11) for camera CC

2

are solved from knowing X(i), Y(i), Z(i) at the 21 locations and the 21 Ui(j), Vi(j) coordinates measured in the calibration photo for the two cameras.

An exemplary set of these three-dimensional positions for right-hand calibration for the calibration fixture with 21 markers appear below:

(1) −3.0 5.0 0.0

(2) −3.0 4.0 0.0

(3) −3.0 3.0 0.0

(4) −3.0 2.0 0.0

(5) 3.0 4.0 1.5

(6) 3.0 3.0 1.5

(7) 3.0 2.0 1.5

(8) 3.0 1.0 1.5

(9) 0.0 5.0 3.0

(10) 0.0 4.0 3.0

(11) 0.0 3.0 3.0

(12) 0.0 2.0 3.0

(13) 0.0 1.0 3.0

(14) 3.0 4.0 4.5

(15) 3.0 3.0 4.5

(16) 3.0 2.0 4.5

(17) 3.0 1.0 4.5

(18) −3.0 5.0 6.0

(19) −3.0 4.0 6.0

(20) −3.0 3.0 6.0

(21) −3.0 2.0 6.0

An exemplary set of these three-dimensional positions for left-hand calibration for the calibration fixture with 21 markers appear below:

(1) 3.0 5.0 6.0

(2) 3.0 4.0 6.0

(3) 3.0 3.0 6.0

(4) 3.0 2.0 6.0

(5) −3.0 4.0 4.5

(6) −3.0 3.0 4.5

(7) −3.0 2.0 4.5

(8) −3.0 1.0 4.5

(9) 0.0 5.0 3.0

(10) 0.0 4.0 3.0

(11) 0.0 3.0 3.0

(12) 0.0 2.0 3.0

(13) 0.0 1.0 3.0

(14) −3.0 4.0 1.5

(15) −3.0 3.0 1.5

(16) −3.0 2.0 1.5

(17) −3.0 1.0 1.5

(18) 3.0 5.0 0.0

(19) 3.0 4.0 0.0

(20) 3.0 3.0 0.0

(21) 3.0 2.0 0.0

The system locates the centers of the spots from the ball fixture

151

by identifying the positions of the pixels in the buffer that have a light intensity greater than a predetermined threshold value. Since the images are two-dimensional, the positions of the pixels have two components (x,y). The system searches the images for bright areas and finds the edges of each of the bright areas. The system then provides a rough estimate of the centers of each of the bright areas. Then all of the bright pixels in each of the bright areas are averaged and an accurate marker position and size are calculated for all 15 areas from the ball fixture. Those with areas smaller than a minimum area are ignored. Once the location of each of the markers on the calibration fixture

151

with respect to cameras BC

1

and BC

2

are determined, the system must know the true spacing of the markers on the calibration fixture

151

. To make this determination for the ball fixture

151

and monitor

16

, the calibration fixture has markers arranged in three rows and five columns. The markers are placed about one inch apart, and on three separate X planes that are 1.5 inches apart. The X, Y, and Z coordinates of the center of each marker

170

a-o

, which are arranged in a three-dimensional pattern, were pre-measured to accuracy of one of one-ten thousandth of an inch on a digitizing table and stored in the computer. The system recalls the previously stored data of the three-dimensional positions of the markers on the calibration fixture relative to one another. The recalled data depends on the whether a right-handed (X-axis points toward the golfer) or a left-handed (X-axis points away from the golfer) system is used. Both sets of data are stored and can be selected by the operator at step S

305

. An exemplary set of these three-dimensional positions for right-hand calibration for the calibration fixture with 15 markers appear below:

(1) −1.5 3.0 0.0

(2) 1.5 3.0 1.0

(3) 0.0 3.0 2.0

(4) 1.5 3.0 3.0

(5) −1.5 3.0 4.0

(6) −1.5 2.0 0.0

(7) 1.5 2.0 1.0

(8) 0.0 2.0 2.0

(9) 1.5 2.0 3.0

(10) −1.5 2.0 4.0

(11) −1.5 1.0 0.0

(12) 1.5 1.0 1.0

(13) 0.0 1.0 2.0

(14) 1.5 1.0 3.0

(15) −1.5 1.0 4.0

An exemplary set of these three-dimensional positions for left-hand calibration for the calibration fixture with 15 markers appear below:

(1) 1.5 3.0 4.0

(2) −1.5 3.0 3.0

(3) 0.0 3.0 2.0

(4) −1.5 3.0 1.0

(5) 1.5 3.0 0.0

(6) 1.5 2.0 4.0

(7) −1.5 2.0 3.0

(8) 0.0 2.0 2.0

(9) −1.5 2.0 1.0

(10) 1.5 2.0 0.0

(11) 1.5 1.0 4.0

(12) −1.5 1.0 3.0

(13) 0.0 1.0 2.0

(14) −1.5 1.0 1.0

(15) 1.5 1.0 0.0

At step S

306

, using the images of the calibration fixture

151

, the system determines eleven (11) constants relating image space coordinates U and V to the known fifteen X, Y, and Z positions on the calibration fixture. The equations relating the calibrated X(I), Y(I), Z(I) spaced points with the U

i

j

, V

i

j

image points are:

\begin{matrix} U_{i}^{j} = \frac{D_{1 j} X (i) + D_{2 j} Y (i) + D_{3 j} Z (i) + D_{4 j}}{D_{9 j} X (i) + D_{10 j} Y (i) + D_{11 j} Z (i) + 1} & (Eq . 3) \end{matrix}

where i=1,15; j=1,2.

\begin{matrix} V_{i}^{j} = \frac{D_{5 j} X (i) + D_{6 j} Y (i) + D_{7 j} Z (i) + D_{8 j}}{D_{9 j} X (i) + D_{10 j} Y (i) + D_{11 j} Z (i) + 1} & (Eq . 4) \end{matrix}

The eleven constants, D

i1

(I=1,11), for camera

136

and the eleven constants, D

i2

(I=1,11), for camera

138

are solved from knowing X(I), Y(I), Z(I) at the 15 locations and the 15 U

i

j

, V

i

j

coordinates measured in the calibration photo for the two cameras.

In another embodiment, during image analysis the system uses the standard Run Length Encoding (RLE) technique to locate the bright areas. The RLE technique is conventional and known by those of ordinary skill in the art. Image analysis can occur during calibration or during an actual shot. Once the bright areas are located using the RLE technique, the system then calculates an aspect ratio of all bright areas in the image to determine which of the areas are the retro-reflective markers. The technique for determining which bright areas are the markers is discussed in detail in below with respect to FIG.

17

.

As noted above, once the system is calibrated in step S

102

, the operator can enter the ambient conditions, including temperature, humidity, wind, elevation, and turf conditions. Next, the operator inputs data about the golfer. For example, the operator enters information about the golfer, including the golfer's name, the test location, gender, age and the golfer's handicap. The operator also identifies the golf ball type and club type, including shaft information, for each test. The operator can also input various hardware set up parameters such as mode of operation (i.e., club and ball data acquisition, club only data acquisition or ball only data acquisition), microphone sensitivity, ball cameras' sensor adjustment, delay times between strobed images of the club and ball in for example microseconds. The particular make of the ball cameras allows software adjustment of the camera sensors the club cameras selected do not have this feature. Another club camera may have this feature. The operator can also input various test setup parameters such as where the data should be stored and a description for the data. In addition, the operator can input system calibration variables such as the accuracy of the club and ball cameras along each axis.

With the calibration complete and reference to

FIGS. 1 and 9

, a golf ball

72

is then set on a tee where the calibration fixture was located (about 40 inches from cameras CC

1

and CC

2

), club

71

is placed behind ball

72

at address and club head

126

on a shaft

128

is swung through three-dimensional club monitor

14

field-of-view. About six inches before the striking of the ball, a light beam between sensor

86

to rod

110

is broken and transmits a signal to open the shutter of camera CC

1

and camera CC

2

and to expose the image sensor panel in cameras CC

1

and CC

2

to light from the three (3) club

71

markers

128

a-c

and six (6) stationary ball markers

134

a-f

. This illumination occurs when the club

71

is a position A. A predetermined time later, such as eight (8) hundred microseconds later, the flash light unit

90

(as shown in

FIG. 4

) fires a flash of light which again illuminates the club

71

markers

128

a-c

and six (6) stationary ball markers

134

a-f

. This occurs when the club

71

is a position B. Although the system can be used with only two flashes of light, more preferably if acceleration data is desired the strobe pulses in succession at least three times so that three images of the club are obtained. As a result, acceleration data can be obtained from two velocity measurements.

Flashes of light are between one-ten thousandth and a few millionths of a second in duration. Very small apertures are used in cameras CC

1

and CC

2

to reduce ambient light and enhance strobe light. As light reflects off markers

128

a-c

in their two positions, it reaches sensor panels forming corresponding panel areas that are digitized and viewable on the computer monitor

22

screen

22

a

. The images from the markers

128

a-c

on the screen are shown as markers

128

a′

-

c′

in

FIGS. 11 and 12

.

Using the known time between camera operation and the known geometric relationships between the cameras, the external computing circuits are able to calculate the X, Y and Z positions of each enhanced marker in a common coordinate system at the time of each snapshot. From the position information and the known data, the external computing circuits are able to calculate the club head velocity and spin (or rotation) in three dimensions during the immediate pre-impact ball

72

launch time period which pre impact condition is determined by calculation based on data from club head positions A and B data and the known position of stationery ball

72

from position B. In addition, the path direction,

attack angle, and hit location are calculable from the position B information provided by the three reflective markers

128

a-c

on club

71

.

As a golfer swings club

71

through the club monitor field-of-view, the system electronic images are seen through the cameras CC

1

and CC

2

as shown on in

FIGS. 11 and 12

. The right hand field-of-view of camera CC

1

(in

FIG. 11

) will differ slightly from the left hand field-of-view of camera CC

2

due to the 20° angle difference in camera orientation. The resulting equations to be solved given the camera coordinates, U

i

(j)

, V

i

(j)

for the three club markers, i, and two cameras j are as follows:

\begin{matrix} U_{i}^{j} = \frac{D_{1 j} X (i) + D_{2 j} Y (i) + D_{3 j} Z (i) + D_{4 j}}{D_{9 j} X (i) + D_{10 j} Y (i) + D_{11 j} Z (i) + 1} & (Eq . 5) \end{matrix}

where i=1,3; j=1,2.

\begin{matrix} V_{i}^{j} = \frac{D_{5 j} X (i) + D_{6 j} Y (i) + D_{7 j} Z (i) + D_{8 j}}{D_{9 j} X (i) + D_{10 j} Y (i) + D_{11 j} Z (i) + 1} & (Eq . 6) \end{matrix}

With the known coordinates X(i), Y(i), Z(i) i=1, 3 for the club

71

in position A, computer

20

further analyzes the positions of X(i), Y(i), Z(i), i=1, 3 at the second position B in FIG.

9

. In addition, the electronic image contains the location of six markers

134

a-f

on golf ball

72

. The triangulation from the data of cameras CC

1

, CC

2

allows us to locate the position of six markers

134

a-f

on the surface of the ball. With information as to the six markers

134

a-f

on the surface and radius of ball

72

, the center of ball

72

, Xc, Yc, Zc are calculated by solving the six (6) equations:

(

X

1

B

−H

C

)

2

+(

Y

i

B

−Y

C

)

2

+(

Z

1

B

−Z

C

)

2

+(RADIUS)

2

I=

1 . . . 6. (Eq. 7)

With the positional information of markers

128

a-c

on the club

71

known, the location of the center of the club face C(C

x

, C

y

, C

z

) and its local coordinate system are found at the two strobed position A and B prior to impact with the ball

72

through the club calibration procedure previously described. The velocity components of the center of club

71

along the

three axis of the coordinate system are then computed from the formulas:

\begin{matrix} V_{x} = \frac{T_{x} (t + Δ T) - T_{x} (t)}{Δ T} & (Eq . 8) \\ V_{y} = \frac{T_{y} (t + Δ T) - T_{y} (t)}{Δ T} & (Eq . 9) \\ V_{z} = \frac{T_{z} (t + Δ T) - T_{z} (t)}{Δ T} & (Eq . 10) \end{matrix}

in which ΔT is the time interval between strobe firings.

The club head spin components result from the matrix of direction cosines relating the orientations of markers

128

a-c

on the club head

126

in one orientation to those in the second orientation. If we denote this matrix by A with elements Aij (i=1,3; j=1,3) then the magnitude, θ, of the angle of rotation vector of the two club head orientations during the time increment ΔT is given by:

\begin{matrix} θ = \sin^{- 1} (\frac{R}{2}) & (Eq . 11) \end{matrix}

l=A

32

−A

23

;

m=A

13

−A

31

; and

n=A

21

−A

12

.

The three orthogonal components of spin rate, W

x

, W

y

W

z

, are given by:

W

x

=sin

−1

(

R/

2)

L

/(

RΔT

)

=θL

/(

RΔT

) (Eq.12)

W

y

=sin

−1

(

R/

2)

M

/(

RΔT

)=θ

M

/(

RΔT

) (Eq.13)

W

z

=sin

−1

(

R/

2)

N

/(

RΔT

)=θ

N

/(

RΔT

) (Eq.14)

From calculating the distance between the center of ball

72

and the center C of the club

71

face minus the radius of ball

72

and the velocity of the center of club face, the time is calculated that it would take the last position of the club face to contact the surface of ball

72

. Knowing this time, the position of the three club head

126

markers

128

a-c

can be calculated assuming the velocity of face remains constant up until it reaches position C when impacting ball

72

. With these club face positions calculated at impact, the position of ball

72

relative to the center of the club face can be calculated by finding the point of intersection of a line through the center of ball

72

and the normal to club face plane found by using the three extrapolated club points

128

a-c.

The path angle and attack angle are found from the components of velocity measured at the center of the face (V

x

,V

y

,V

z

). They are defined as follows:

Path Angle=tan

−1

(

V

x

/V

z

) (Eq.15)

Attack Angle=tan

−1

(

V

y

/[V

x

2

=V

z

2

]) (Eq.16)

With the automatic location of club velocity, path angle, attack angle and face hit location, the golfer receives quantitative information on his swing for teaching and club fitting purposes. In addition, the direction of the club face plane can be calculated at impact.

EXAMPLE

After calibration a described above a golfer swung an iron through field-of-view striking balls

72

. The following data was obtained:

TABLE 1

Club Monitor Data

Parameter

Measurement

Club head speed perpendicular to

100.1

intended line of flight of ball (mph)

Loft Angle (degrees)

19.2

Attack Angle (degrees)

3.8 Down

Path Angle (degrees)

2.1 In-to-Out

Face Angle (degrees)

3.4 Open

Droop angle (degrees)

−3.7

Loft Spin (rpm)

159

Face Spin (rpm)

333

Droop Spin (rpm)

87

Hit-Vertical (inches)

.14 below geometric center

Hit-Horizontal (inches)

.31 from geometric center

toward heel

Based on the information in Table 1, the golfer should be advised to swing the golf club higher and to close the golf club face sooner before impact.

Additional data that is useful to the operator that can be obtained is the distance of the club head from the ball at position B. If this distance is zero or less than zero, it means the club head has contacted the ball at position B and thus the measurements do not reflect true velocity and should be retaken.

Referring to

FIGS. 1 and 10

, after the club head is swung and impacts the ball the ball monitor

16

is triggered when a sound trigger from the club hitting the golf ball is sent via microphone

122

to the system. The strobe light unit within the ball monitor

14

is activated causing a first image to be recorded by both cameras BC

1

, BC

2

at position D in FIG.

10

. There is an intervening, predetermined time delay, preferably 800 microseconds, before the strobe light flashes again and a second image of the ball is captured by cameras BC

1

and BC

2

at position D. The images from the markers

128

a-c

on the screen are shown as markers

134

a′

-

f′

in

FIGS. 13 and 14

.

The time delay is limited on one side by the ability to flash the strobe light and on the other side by the field-of-view. If the time delay is too long, the field-of-view may not be large enough to capture the golf ball in the cameras' views for both images. The cameras used in the systems

10

and

100

allow for both images (which occur during the first and the second strobe flashes) to be recorded in one image frame. Because the images are recorded when the strobe light flashes (due to reflections from the retro-reflective material on the golf ball), the flashes can be as close together as needed without concerns for the constraints of a mechanically shuttered camera.

This sequence produces an image of the reflections of light off of the retro-reflective markers on each light sensitive panel of the cameras and is shown in the monitor from camera BC

1

in FIG.

13

and BC

2

in FIG.

14

. The location of the markers in each of the images are preferably determined with the RLE technique which was discussed for the calibration fixture.

The technique used for determining the aspect ratio to determine which bright areas are markers will now be described in conjunction with FIG.

17

. As shown in step S

401

, the image must have an appropriate brightness threshold level chosen. By setting the correct threshold level for the image to a predetermined level, all pixels in the image are shown either as black or white. Second, at step S

402

, the images are segmented into distinct segments, corresponding to the bright areas in each of the images. The system, at step S

403

, determines the center of each area by first calculating the following summations at each of the segments using the following equations:

S

x

=ΣX

i

(Eq. 17)

S

xx

=ΣX

i

2

(Eq. 19)

S

yy

=ΣY

i

2

(Eq. 20)

S

xy

=ΣX

i

Y

i

(Eq. 21)

Once these sums, which are the sums of the bright areas, have been accumulated for each of

S

y

=ΣY

i

(Eq. 18)

the segments in the image, the net moments about the x and y axes are calculated using the following equations:

\begin{matrix} I_{x} = S_{xx} - \frac{S_{x}^{2}}{AREA} & (Eq . 22) \\ I_{y} = S_{yy} - \frac{S_{y}^{2}}{AREA} & (Eq . 23) \\ I_{xy} = S_{xy} - \frac{S_{x} S_{y}}{AREA} & (Eq . 24) \end{matrix}

where AREA is the number of pixels in each bright area.

At step S

404

, the system eliminates those areas of brightness in the image that have an area outside a predetermined range. Thus, areas that are too large and too small are eliminated. In the preferred embodiment, the markers on the golf ball are ¼″-⅛″ and the camera has 753×244 pixels, so that the markers should have an area of about 105 pixels in the images. However, glare by specular reflection, including that from the club head and other objects, may cause additional bright areas to appear in each of the images. Thus, if the areas are much less or much more than 105 pixels, then the system can ignore the areas since they cannot be a marker on the golf ball.

For those areas that remain (i.e., that are approximately 105 pixels) the system determines which are the correct twelve in the following manner. The system assumes that the markers will leave an elliptical shape in the image due to the fact that the markers are round and the golf ball's movement during the time that the strobe light is on. Therefore, at step S

405

the system then calculates the principal moments of inertia of each area using the following equations:

\begin{matrix} I_{x^{'}} = \frac{I_{x} + I_{y}}{2} + \sqrt{{(\frac{I_{x} - I_{y}}{2})}^{2} + I_{xy}^{2}} & (Eq . 25) \\ I_{y^{'}} = \frac{I_{x} + I_{y}}{2} - \sqrt{{(\frac{I_{x} - I_{y}}{2})}^{2} + I_{xy}^{2}} & (Eq . 26) \end{matrix}

These moments are converted to the golf ball reference frame in step

406

. Finally, at step S

407

the aspect ratio is calculated using the following equation:

\begin{matrix} R = \frac{I_{x^{'}}}{I_{y^{'}}} & (Eq . 27) \end{matrix}

and the marker is rejected at step S

408

if the aspect ratio is greater than four or five.

Returning to

FIG. 15

, once the locations of the markers are determined, the system computes the translational velocity of the center of the golf ball and angular velocity (spin rate) of the golf ball at step S

107

in the following manner. First, the system uses the triangulation from the data of cameras to locate the position of the six markers on the surface of the golf ball. Specifically, the system solves the set of four linear equations shown below to determine the position (x,y,z) in the golf ball's coordinate system of each marker on the surface of the golf ball.

(

D

9,1

U

1

−D

1,1

)

x+

(

D

10,1

U

1

−D

2,1

)

y+

(

D

11,1

U

1

−D

3,1

)

z+

(

U

1

−D

4,1

)=0 (Eq.28)

(

D

9,1

V

1

−D

5,1

)

x+

(

D

10,1

V

1

−D

6,1

)

y+

(

D

11,1

V

1

−D

7,1

)

z+

(

V

1

−D

8,1

)=0 (Eq.29)

(

D

9,2

U

2

−D

1,2

)

x+

(

D

10,2

U

2

−D

2,2

)

y+

(

D

11,2

U

2

−D

3,2

)

z+

(

U

2

−D

4,2

)=0 (Eq.30)

(

D

9,2

V

2

−D

5,2

)

x+

(

D

10,2

V

2

−D

6,2

)

y+

(

D

11,2

V

2

−D

7,2

)

z+

(

V

2

−D

8,2

)=0 (Eq.31)

where D

ij

are the eleven constants determined by the calibration method at steps S

102

and S

306

(FIG.

16

), where i identifies the constant and j identifies the image.

Next, the system converts the marker locations (determined at step S

306

in

FIG. 16

) in the golf ball coordinate system to the reference global system of the calibrated cameras BC

1

, BC

2

using the following matrix equation:

\begin{matrix} [\begin{matrix} x_{g} \\ y_{g} \\ z_{g} \end{matrix}] = [\begin{matrix} T_{x} \\ T_{y} \\ T_{z} \end{matrix}] + [\begin{matrix} M_{11} M_{12} M_{13} \\ M_{21} M_{22} M_{23} \\ M_{31} M_{32} M_{33} \end{matrix}] [\begin{matrix} x_{b} \\ y_{b} \\ z_{b} \end{matrix}] & (Eq . 32) \end{matrix}

where Xg, Yg, Zg are the global coordinates of the center of the golf ball. The column vector, T

x

,T

y

,T

z

, is the location of the center of the golf ball in the global coordinate system. The matrix elements M

ij

(i=1,3;j=1,3) are the direction cosines defining the orientation of the golf ball coordinate system relative to the global system. The three angles a

1

,a

2

,a

3

describe the elements of matrix M

ij

in terms of periodic functions. Substituting matrix equation for the global position of each reflector into the set of four linear equations shown above, a set of 28 equations result for the six unknown variables (T

x

,T

y

,T

z

,a

1

,a

2

,a

3

). A similar set of 28 equations must be solved for the second image of the golf ball. Typically, the solution of the three variables T

x

,T

y

,T

z

and the three angles at a

1

,a

2

,a

3

that prescribed the rotation matrix M is solvable in four iterations for the 28 equations that must be simultaneously satisfied.

The kinematic variables, three components of translational velocity and three components of angular velocity in the global coordinate system, are calculated from the relative translation of the center of mass and relative rotation angles that the golf ball makes between its two image positions.

The velocity components of the center of mass V

x

,V

y

,V

z

along the three axes of the global coordinate system are given by the following equations:

\begin{matrix} V_{x} = \frac{T_{x} (t + Δ T) - T_{x} (t)}{Δ T}; & (Eq . 33) \\ V_{y} = \frac{T_{y} (t + Δ T) - T_{y} (t)}{Δ T}; & (Eq . 34) \\ V_{z} = \frac{T_{z} (t + Δ T) - T_{z} (t)}{Δ T} & (Eq . 35) \end{matrix}

(Eqs. 33, 34, and 35, respectively) in which t is the time of the first strobe measurement of T

x

,T

y

,T

z

and ΔT is the time between images.

The spin rate components in the global axis system result from obtaining the product of the inverse orientation matrix, M

T

(t) and M(t+ΔT). The resulting relative orientation matrix, A, A(t,t+Δt)=M(t+Δt)M

T

(t), measures the angular difference of the two strobe golf ball images.

The magnitude Θ of the angle of rotation about the spin axis during the time increment ΔT is given by equation Eq. 11. The three orthogonal components of spin rate, W

x

,W

y

,W

z

are given by the equation Eqs. 12-14.

At step S

109

of

FIG. 15

, the system, including a computer algorithm, then computes the trajectories for the tests using the initial velocity and initial spin rate which were computed in step S

107

. For each time increment, the system interpolates the forces on the golf ball at time T and calculates the velocity at time T+1 from the velocity of the golf ball and the forces on the golf ball at time T. Next, the system computes the mean velocity and the Reynold's number, which is the ratio of the flow's inertial forces to the flow's viscous forces during the time interval from time T to time T+1. The system then interpolates the mean forces, from which the system calculates the velocity at time T+1. The forces include the drag force, the lift due to the spin of the golf ball, and gravitational forces. Using the velocity at time T+1, the system can compute the position at time T+1. Finally, the system computes the spin rate at time T+1. In the preferred embodiment, the length of the time interval is 0.1 seconds. This calculation is performed until the golf ball reaches the ground.

The system uses the equations in U.S. application Ser. No. 09/156,611 to perform these calculations. Accordingly, the system computes the total distance from the tee to the final resting position of the golf ball. A data file stores the results computed by the trajectory method.

Referring again to

FIG. 15

, the system then determines whether an additional test will be performed. If additional tests are to be performed, the process described above repeats, beginning at step S

104

with the sound trigger through step S

110

where the trajectory method computes and presents the trajectory for the golf ball.

When all tests have been performed, the analysis method computes statistics for each golf ball type used in the tests and presents the results to the operator. For the group of tests performed for each golf ball type, the system computes the average value and standard deviation from the mean for several launch characteristics including the velocity, the launch angle, the side angles, the backspin, the side spin, and the carry and roll.

Different factors contribute to the standard deviation of the measurements including the variation in the compression and resilience of the golf balls, the variation in the positioning of the markers on the golf balls, the pixel resolution of the light sensitive panels and the accuracy of the pre-measured markers on the calibration fixture. Obviously, the primary source of scatter lies in the swing variations of the typical golfer.

Upon request from the operator, the system will display the test results in various forms. For example, the system will display individual results for the golf ball type selected by the operator. The following table shows sample data obtained during the same swing as the club head data obtained in Table 1:

TABLE 2

Ball Monitor Data

Parameter

Measurement

Speed of Ball (mph)

139.7

Launch Angle (degrees)

14.4

Backspin (rpm)

5512

Side Angle (degrees)

.7 Push

Side Spin (rpm)

1135 Slice

Rifling Spin (rpm)

682

Carry Distance (yards)

203.5

Deviation (yards) - the distance and direction the ball

25.0 Right

deviates from a straight flight path

Carry and Roll Distance (Yards)

215.0

Based on the information in Table 2, the golfer should be advised to close the club face more at impact to avoid the slice and to swing in-to-out so to avoid a push.

Similarly, the system in step S

113

can also display tabular representations of the trajectories for the golf ball types selected by the operator. The tabular representation presents trajectory information including distance, height, velocity, spin, lift, drag, and the Reynold's number. Similarly, the analysis method displays graphical representation of the trajectories for the golf ball types selected by the operator. The system computes the graphical trajectories from the average launch conditions computed for each golf ball type.

At step S

113

, the system displays the average of each of the shots taken by the golfer. The results are displayed in a tabular and/or graphical format. The displayed results include the total distance, the spin rate, the launch angle, distance in the air, and golf ball speed. From this information, the system at step S

114

shows the golfer the results if the launch angle and spin rate of the golf ball were slightly changed, allowing the golfer to optimize the equipment and/or swing. Results could also be changed and displayed based on changes in the club speed and angles.

At step S

114

, the system calculates the distances of a golf ball struck at a variety of launch angles and spin rates that are close to those for the golfer. The operator is able to choose which launch angles and spin rates are used to calculate the distances. In order to display this particular data, the system performs the trajectory calculations described above between about 50-100 times (several predetermined values of launch angles and several predetermined values of initial spin rates). The operator can dictate the range of launch angles and spin rates the system should use, as well as how many values of each the system uses in the calculations. From the graphical data (*), the golfer can determine which of these two variables could be changed to improve the distance.

Since the golfer's data is saved, when the system is in the test mode, it is also possible to compare the golfer's data with that of other golfers, whose data were also saved. In this way, it is possible for golfers to have their data (launch angle, initial golf ball speed, spin rate, etc.) compared to others. This comparison may be done in a tabular or graphical format. Similarly, the system may compare the data from successive clubs (e.g., a 5-iron to a 6-iron to a 7-iron) to determine if there are gaps in the clubs (inconsistent distances between each of the clubs). Alternatively, two different golfers could be compared using the same or different clubs, or the same or different balls.

The club cameras can include filters of a different color from filters on the ball camera. For example, the club cameras can include different color filters and the club and ball can include different colored markers. The net effect should be that the club cameras record images of the markers on the club and ball and the ball cameras record only images of the markers on the ball not the club. Alternatively to using different color filters and markers, dimmer markers can be used on the club with a strong strobe light in the club monitor and brighter markers can be used on the ball with a weak strobe light in the ball monitor. The net result, will be the same as with the colored filters and balls (i.e., the club image has club and ball markers and the ball image has only ball markers).

While the above invention has been described with reference to certain preferred embodiments, it should be kept in mind that the scope of the present invention is not limited to these embodiments. The system can also be set up to measure the golfer's swing during the back swing, down swing and/or both. The system is shown with two club cameras and two ball cameras, a single club camera and a single ball camera can be used but accuracy of the measurements decreases with only two cameras. The single club and ball camera system can be used with any of the lighting arrangements discussed above, such as with dual adjacent strobe lights. The embodiments above can also be modified so that some features of one embodiment are used with the features of another embodiment. One skilled in the art may find variations of these preferred embodiments which, nevertheless, fall within the spirit of the present invention, whose scope is defined by the set forth below.

Number	Name	Date	Kind
4063259	Lynch et al.	Dec 1977	A
4136387	Sullivan et al.	Jan 1979	A
4713686	Ozaki et al.	Dec 1987	A
5342054	Chang et al.	Aug 1994	A
5471383	Gobush et al.	Nov 1995	A
5575719	Gobush et al.	Nov 1996	A
6011359	Days	Jan 2000	A
6042483	Katayama	Mar 2000	A
6241622	Gobush et al.	Jun 2001	B1
6431990	Manwaring	Aug 2002	B1
6565448	Cameron et al.	May 2003	B2

Launch monitor system and a method for use thereof

Information

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Date Filed

Date Issued

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Agents

CPC

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US Referenced Citations (11)