DETERMINATION OF SPIN PARAMETERS OF A SPORTS BALL

• US 20160067581A1
• Filed: 09/05/2014
• Published: 03/10/2016
• Est. Priority Date: 03/03/2005
• Status: Active Grant

• Current Assignee: Trackman A/S
• Original Assignee: Trackman A/S
• Inventors: Tuxen, Fredrik
• Granted Patent: US 9,645,235 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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
• CPC Class Codes: G01S 13/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 13/88 Radar or analogous systems specially adapted for specific applications electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00

Abstract

A method of determining spin parameters of a sports 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. A method of estimating a spin frequency of an unmarked rotating sports ball in flight, the method comprising:

receiving, using a receiver of a radar arrangement, electromagnetic waves reflected from the unmarked rotating sports ball;

deriving from said received electromagnetic waves, via the radar arrangement, a signal having a first frequency corresponding to a velocity of the unmarked rotating sports ball, the signal being amplitude modulated by a modulation frequency; and

estimating, via the radar arrangement, at at least a single point in time, the spin frequency of the unmarked rotating sports ball based on at least one frequency distance between a harmonic of the modulation frequency and one or more of;

in a first case, the first frequency and, in a second case, an additional harmonic of the modulation frequency.

2. The method of claim 1, wherein the spin frequency is determined by dividing the frequency distance by a harmonic number of the harmonic in the first case or a difference in harmonic number of the harmonics in the second case.

3. The method of claim 1, wherein the deriving step includes performing a frequency analysis of the signal.

4. The method according to claim 3, wherein the step of performing the frequency analysis comprises detecting a plurality of harmonics.

5. The method of claim 1, wherein said harmonic and said additional harmonic comprise harmonics symmetric about the first frequency.

6. The method of claim 1, wherein said first harmonic and said additional harmonic comprise two adjacent harmonics.

7. The method of claim 1, wherein the spin frequency of the rotating sports ball is estimated based on the at least one frequency distance between the first frequency and each of said harmonic and said additional harmonic.

8. The method according to claim 1, wherein the first frequency corresponds to the velocity of the rotating sports ball in a direction toward or away from the receiver.

9. The method of claim 1, wherein said estimating step is repeated at at least one additional point in time during the flight of the rotating sports ball.

10. The method of claim 3, wherein the step of performing a frequency analysis comprises:

identifying the first frequency as a 0^th harmonic, the first frequency corresponding to the velocity of the rotating sports ball in a direction toward or away from the receiver,

tracking a plurality of harmonics of the modulation frequency of said signal over time,

qualifying the tracked plurality of harmonics by requiring that the tracked plurality of harmonics are equally spaced in frequency, and

solving the qualified harmonics for their corresponding harmonic number,

wherein the step of estimating comprises estimating, at at least one point in time, the spin frequency from two of the qualified harmonics by dividing the frequency distance by a difference between respective corresponding harmonic numbers of said two qualified harmonics.

11. A system for estimating a spin frequency of an unmarked rotating sports ball in flight, the system comprising:

a receiver of a radar arrangement configured to, at at least a single point in time, receive electromagnetic waves reflected from the unmarked rotating sports ball and provide a corresponding signal, which is amplitude modulated by a modulation frequency,

wherein the radar arrangement is configured to perform a frequency analysis of the amplitude modulated signal and detect at least one harmonic of the modulation frequency, the radar arrangement being further configured to estimate the spin frequency from a frequency distance between said at least one harmonic and one or more of;

in a first case, a first frequency corresponding to a velocity of the unmarked rotating sports ball and, in a second case, an additional harmonic of the modulation frequency.

12. A system according to claim 11, wherein the spin frequency is determined by dividing the frequency distance by a harmonic number of the harmonic in the first case or a difference in harmonic number of the harmonics in the second case.

13. A system according to claim 11, wherein the radar arrangement is further configured to

identify, subsequent to the frequency analysis, the first frequency as a 0^th harmonic, the first frequency corresponding to the velocity of the rotating sports ball in a direction toward or away from the receiver,

track a plurality of harmonics of the modulation frequency of said signal over time,

qualify the tracked plurality of harmonics by requiring that the tracked plurality of harmonics are equally spaced in frequency,

solve the qualified harmonics for their corresponding harmonic number, and

estimate the spin frequency from two of the qualified harmonics by dividing the frequency distance by a difference between respective corresponding harmonic numbers of said two qualified harmonics.

14. The system of claim 11, wherein said at least one harmonic and said additional harmonic comprise two adjacent harmonics.

15. The system of claim 11, wherein said at least one harmonic and said additional harmonic comprise harmonics symmetric about the first frequency.

16. The system of claim 11, wherein the spin frequency of the rotating sports ball is estimated based on the frequency distance between the first frequency and each of said at least one harmonic and said additional harmonic.

17. The system of claim 11, wherein the first frequency corresponds to the velocity of the rotating sports ball in a direction toward or away from the receiver.

18. A system for estimating a spin frequency of an unmarked rotating sports ball in flight, the system comprising:

a receiver of a radar arrangement; and

a computer-readable medium storing instructions which, when executed on the receiver, cause the receiver to perform operations comprising;

receiving electromagnetic wave reflected from the unmarked rotating sports ball;

deriving, from the electromagnetic waves, a signal having a first frequency corresponding to a velocity of the unmarked rotating sports ball, the signal being amplitude modulated by a modulation frequency; and

estimating, at a point in time, the spin frequency of the unmarked rotating sports ball based on a frequency distance between a harmonic of the modulation frequency and one of the first frequency and an additional harmonic of the modulation frequency.

19. The system of claim 18, wherein the spin frequency is determined by dividing the frequency distance by one of a harmonic number of the harmonic and a difference in harmonic number of the harmonics.

20. The system of claim 18, wherein the deriving of the signal further comprises performing a frequency analysis of the signal.