System and method for determining a spin axis of a sports ball

Patent metadata

Field	Value
Publication number	US-11938375-B2
Application number	US-202217819098-A
Country	US
Kind code	B2
Filing date	Aug 11, 2022
Priority date	Mar 13, 2018
Publication date	Mar 26, 2024
Grant date	Mar 26, 2024

Abstract

A system determining a spin axis of a ball includes a radar transmitting a signal into a target area. The radar includes a minimum of three receivers arranged so that two pairs of receivers are not co-linear. The system also includes a Processing Unit (“PU”) receiving data from the radar and determining a radar range of frequencies received at a point in time corresponding to differing velocities relative to the radar of different portions of the ball as the ball is spinning. PU divides the radar frequency range into a plurality of frequency components and calculating, for each of the frequency components, an angular position associated therewith. PU identifies as a projection of the spin axis in a plane perpendicular to a line of sight from the radar to the ball, a line perpendicular to a line represented by the determined angular positions.

First claim

What is claimed is:

1. A method for determining a spin axis of a sports ball, comprising:
transmitting a signal, via a first radar, into a target area into which the sports ball is to be launched, the first radar including three receivers arranged so that a minimum of three receivers are not co-linear, the signal being reflected back to the receivers by the sports ball;
receiving, by the first radar, the received reflected signal via the receivers;
performing a frequency analysis on the received reflected signal received by the first radar at a first point in time to determine a frequency spectrum comprising a range of frequencies received by the first radar corresponding to differing velocities relative to the first radar of different portions of the sports ball as the sports ball is spinning;
separating the determined frequency spectrum into a plurality of frequency components; and
determining for each of the frequency components a first phase difference between signals received at a first pair of the three receivers and a second phase difference between signals received at a second pair of the three receivers and identifying a component of the spin axis of the sports ball based on the determined first and second phase differences.

2. The method of claim 1 , wherein the component of the spin axis is identified as a projection of the spin axis of the sports ball onto a plane perpendicular to a line of sight from the first radar to the sports ball.

3. The method of claim 2 , wherein the projection of the spin axis of the sports ball is identified as a line perpendicular to a line represented by the determined first and second phase differences.

4. The method of claim 1 , further comprising performing a motion compensation of the received reflected signal to subtract an average motion of the sports ball from the signal.

5. The method of claim 4 , wherein the motion compensation centers the received reflected signal around 0 Hz.

6. A method for determining a spin axis of a sports ball, comprising:
transmitting a signal, via a first radar, into a target area into which the sports ball is to be launched, the first radar including three receivers arranged so that a minimum of three receivers are not co-linear, the signal being reflected back to the receivers by the sports ball;
receiving, by the first radar, the received reflected signal via the receivers;
performing a frequency analysis on the received reflected signal received by the first radar at a first point in time to determine a frequency spectrum comprising a range of frequencies received by the first radar corresponding to differing velocities relative to the first radar of different portions of the sports ball as the sports ball is spinning;
separating the determined frequency spectrum into a plurality of frequency components; and
identifying for each of the frequency components a velocity contour line on a surface of the sports ball, each velocity contour line corresponding to a plurality of reflection points on the surface of the sports ball with the same relative velocity based on a phase difference detected between signals received by a first pair of the receivers of the first radar and signals received by a second pair of the receivers of the first radar.

7. The method of claim 6 , further comprising identifying as a projection of the spin axis of the sports ball onto a plane perpendicular to a line of sight from the first radar to the sports ball, a line perpendicular to a line represented by the determined phase differences.

8. The method of claim 6 , further comprising averaging locations positioned on each contour line to define a point within the corresponding plane, a set of points from each velocity contour line corresponding to a line perpendicular to the spin axis.

9. A method for determining a spin axis of a sports ball, comprising:
transmitting a signal, via a first radar, into a target area into which the sports ball is to be launched, the first radar including three receivers arranged so that a minimum of three receivers are not co-linear, the signal being reflected back to the receivers by the sports ball;
receiving, by the first radar, the received reflected signal via the receivers; and
performing a frequency analysis on the received reflected signal received by the first radar and, based on the frequency analysis, calculating a derivative of phase differences observed at the receivers with respect to frequency and, based on this derivative, identifying a spin axis of the sports ball.

10. The method of claim 9 , further comprising, based on the phase differences relative to the first radar, determining the spin axis of the sports ball in a world coordinate system.

11. The method of claim 9 , further comprising determining aerodynamical effects on a flight path of the sports ball based on the identified spin axis of the sports ball and a spin rate of the sports ball.

12. The method of claim 11 , further comprising generating a simulated projection of a continued flight path of the sports ball after the determination of the spin axis.

13. The method of claim 12 , further comprising providing to a camera operator an illustrated flight path of the sports ball to enhance tracking of the sports ball via a camera.

14. The method of claim 12 , further comprising automatically controlling a camera to track the sports ball based on the simulated projection of the continued flight path of the sports ball.

15. The method of claim 9 , further comprising deriving a first spin axis of the sports ball at a first point in time and a second spin axis of the sports ball at a second point in time and combining the first and second spin axes to determine a three-dimensional spin axis for the sports ball.

16. The method of claim 15 , wherein the first and second spin axes of the sports ball are combined to determine the three-dimensional spin axis for the sports ball based on an assumption that gyroscopic effects render a orientation of the three-dimensional spin axis in a world coordinate system substantially constant over time.

17. The method of claim 9 , wherein the spin axis of the sports ball is identified as a derivative vector of the phase difference with respect to frequency of a Doppler signal received from the sports ball.

18. A method for determining a spin axis of a sports ball, comprising:
transmitting a signal, via a first radar, into a target area into which the sports ball is to be launched, the first radar including three receivers arranged so that a minimum of three receivers are not co-linear, the signal being reflected back to the receivers by the sports ball;
receiving, by the first radar, the received reflected signal via the receivers; and
performing a frequency analysis on the received reflected signal received by the first radar and, based on the frequency analysis, calculating a derivative of differences of a time of receipt of signals at the three receivers with respect to frequency and, based on these derivatives, identifying a component of the spin axis of the sports ball based on the determined derivative.

19. The method of claim 18 , wherein the component of the spin axis is identified as a projection of the spin axis of the sports ball onto a plane perpendicular to a line of sight from the first radar to the sports ball.

20. The method of claim 19 , wherein the projection of the spin axis of the sports ball is identified as a line perpendicular to a line represented by the determined derivatives.

21. The

Assignees

• Trackman As

Inventors

• Tuxen Fredrik
• Ungstrup Michael
• Mackeprang Kasper

Classifications

• A63B24/0021 Primary

  Tracking a path or terminating locations · CPC title

• A63B69/3658

  Means associated with the ball for indicating or measuring, e.g. speed, direction · CPC title

• G01S13/58

  Velocity or trajectory determination systems; Sense-of-movement determination systems · CPC title

• G01S13/583 Primary

  using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves and based upon the Doppler effect resulting from movement of targets · CPC title

• G01S13/88 Primary

  Radar or analogous systems specially adapted for specific applications (electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00) · CPC title