Determination of spin parameters of a sports ball
AssigneeTrackman A/S
InventorFredrik Tuxen
Life of this patent
Estimating the term…
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.
Claims20
A method for estimating a spin axis of a sports ball in flight at a sensor arrangement comprising at least a first sensor and processor, comprising:
- capturing, by the first sensor, data corresponding to the sports ball;
- deriving, from portions of the data captured without regard to any marking on the sports ball, a signal having a first frequency corresponding to a velocity of the sports ball, the signal being modulated by a modulation frequency;
- and
- estimating, at at least a single point in time, a spin frequency of the sports ball based at least on the modulation frequency;
- wherein the processor performs calculations comprising:
- (1) determining at least part of a 3D-trajectory of the sports ball from either one of the data captured from the first sensor or further data corresponding to the sports ball captured from a second sensor;
- (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 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 and the estimated spin frequency.
A system for estimating a spin axis of a sports ball in flight, comprising:
- a first sensor configured to capture data corresponding to the sports ball;
- and
- a processor configured to:
- derive, from portions of the data captured without regard to any marking on the sports ball, a signal having a first frequency corresponding to a velocity of the sports ball, the signal being modulated by a modulation frequency;
- and
- estimate, at at least a single point in time, a spin frequency of the sports ball based at least on the modulation frequency;
- wherein the processor is further configured to:
- (1) determine at least part of a 3D-trajectory of the sports ball from either one of the data captured from the first sensor or further data corresponding to the sports ball captured from a second sensor;
- (2) estimate, from the trajectory, an acceleration A of the sports ball at a predetermined position along the trajectory;
- (3) estimate an acceleration G of the sports ball caused by gravity at the predetermined position;
- (4) estimate an air speed vector Vair at the predetermined position;
- (5) estimate an acceleration D of the sports ball caused by air resistance at the predetermined position from D=[(A−G)*Vair/|Vair|2]*Vair;
- and
- (6) estimate the spin axis, at the predetermined position, on the basis of the estimated accelerations and the estimated spin frequency.
Dependencies are inferred from the claim text.