DETERMINATION OF SPIN PARAMETERS OF A SPORTS BALL

• US 20090075744A1
• Filed: 02/28/2006
• Published: 03/19/2009
• Est. Priority Date: 03/03/2005
• Status: Active Grant

• Current Assignee: Trackman A/S
• Original Assignee: Interactive Sports Games A/S
• Inventors: Tuxen, Fredrik
• Granted Patent: US 8,845,442 B2
• Time in Patent Office: Days
• US Class Current: 473/200
• CPC Class Codes: A63B 2024/0034 during flight
• CPC Class Codes: A63B 2220/35 Spin
• CPC Class Codes: A63B 24/0021 Tracking a path or terminating locations
• CPC Class Codes: A63B 69/3658 Means associated with the ball for indicating or measuring, e.g. speed, direction

Abstract

A method of determining spin parameters of a spot ball, such as spin axis and rotation velocity of a golf ball. The spin axis is determined solely from the trajectory of the flying ball, and the rotational velocity is determined from a frequency analysis of a signal provided by a radar, which signal comprises spectrum traces positioned equidistantly in frequency, which frequency distance relates to the spin velocity.

Claims

1-16. -16. (canceled)

17. A method of estimating a rotational velocity or spin frequency of a rotating sports ball in flight, the method comprising:

1. a number of points in time during the flight, receiving electromagnetic waves reflected from the rotating sports ball and providing a corresponding signal,

2. performing a frequency analysis of the signal, and identifying one, two or more discrete spectrum traces positioned at least substantially equidistantly in frequency and being continuous over time, and

3. estimating the velocity/frequency from a frequency distance between the discrete spectrum traces.

18. A method according to claim 17, wherein step 1. comprises receiving the reflected electromagnetic waves using a receiver, and wherein step 2. comprises identifying, subsequent to the frequency analysis, a first frequency corresponding to a velocity of the ball in a direction toward or away from the receiver and wherein identification of the spectrum traces comprises identifying spectrum traces positioned symmetrically around the first frequency.

19. A method according to claim 17, wherein step 2. comprises, for each point in time and sequentially in time:

performing the frequency analysis and an identification of equidistant candidate frequencies for a point in time,

subsequently identifying those candidates which each has a frequency deviating at the most a predetermined amount from a frequency of a candidate of one or more previous points in time,

then identifying, as the frequency traces, traces of identified candidates, and where step 3 comprises estimating the velocity/frequency on the basis of the identified spectrum traces.

20. A system for estimating a rotational velocity or spin frequency of a rotating sports ball in flight, the system comprising:

1. a receiver adapted to, a number of points in time during the flight, receive electromagnetic waves reflected from the rotating sports ball and provide a corresponding signal,

2. means for performing a frequency analysis of the signal, and identifying one, two or more discrete spectrum traces positioned at least substantially equidistantly in frequency and being continuous over time, and

3. means for estimating the velocity/frequency from a frequency distance between the discrete spectrum traces.

21. A system according to claim 20, wherein the means 2. are adapted to identify, subsequent to the frequency analysis, a first frequency corresponding to a velocity of the ball in a direction toward or away from the receiver and to identify, as the spectrum traces, spectrum traces positioned symmetrically around the first frequency.

22. A system according to claim 20, wherein the means 2. are adapted to, for each point in time and sequentially in time:

perform the frequency analysis and the identification of equidistant candidate frequencies for a point in time,

subsequently identify those candidates which have a frequency deviating at the most a predetermined amount from a frequency of a candidate of one or more previous points in time,

then identify, as the frequency traces, traces of identified candidates, and where the means 3 are adapted to estimate the velocity/frequency on the basis of the identified spectrum traces.

23. A method of estimating a spin axis of a sports ball while in flight, the method comprising:

1. determining at least part of a 3D-trajectory of the flying sports ball,

2. estimating, from the trajectory, an acceleration, A, of the sports ball at a predetermined position along the trajectory,

3. estimating an acceleration, G, of the sports ball caused by gravity at the predetermined position,

4. estimating an air speed vector, Vair, at the predetermined position,

5. estimating an acceleration, D, of the sports ball caused by air resistance/drag at the predetermined position, from D=[(A−

G)•

Vair/|Vair|²]*Vair and

6. estimating the spin axis, at the predetermined position, on the basis of the estimated accelerations.

24. A method according to claim 23, wherein steps 2-5 are performed at each of a plurality of points in time.

25. A method according to claim 23, wherein step 6. comprises subtracting the accelerations estimated in steps 3. and 5. from that estimated in step 2, determining a residual acceleration, and estimating the spin axis on the basis of a direction of the residual acceleration.

26. A method according to claim 23, wherein step 5 comprises estimating a velocity of the ball at the predetermined position from the trajectory and estimating the acceleration on the basis of the estimated velocity.

27. A system for estimating a spin axis of a sports ball while in flight, the system comprising:

1. means for determining at least part of a 3D-trajectory of the flying sports ball,

2. means for estimating, from the trajectory, an acceleration, A, of the sports ball at a predetermined position along the trajectory,

3. means for estimating an acceleration, G, of the sports ball caused by gravity at the predetermined position,

4. means for estimating an air velocity vector, Vair, at the predetermined position,

5. means for estimating an acceleration, D, of the sports ball caused by air resistance/drag at the predetermined position, from D=[(A−

G)•

Vair/|Vair|²]*Vair, and

6. means for estimating the spin axis, at the predetermined position, on the basis of the estimated accelerations.

28. A system according to claim 27, wherein the means 2-5 are adapted to estimate the accelerations at each of a plurality of predetermined positions.

29. A system according to claim 27, wherein means 6. are adapted to subtract the accelerations estimated in steps 3. and 5. from that estimated in step 2, determine a residual acceleration, and estimate the spin axis on the basis of a direction of the residual acceleration.

30. A system according to claim 27, wherein the means 5 are adapted to estimate a velocity of the ball at the predetermined position from the trajectory and estimate the acceleration on the basis of the estimated velocity.