Swing quality measurement system
A system that measures a swing of a bat with one or more sensors and analyzes sensor data to create swing quality metrics. Metrics may include for example rotational acceleration, on-plane efficiency, and body-bat connection. Rotational acceleration measures the centripetal acceleration of the bat along the bat's longitudinal axis at a point early in the rotational part of the swing; it is an indicator of the swing's power. On-plane efficiency measures how much of the bat's angular velocity occurs around the swing plane, the plane spanned by the bat and the bat's sweet spot velocity at impact. Body-bat connection measures the angle between the bat and the body tilt axis, which is estimated from the trajectory of the hand position on the bat through the swing; an ideal bat-body connection is near 90 degrees. These three swing quality metrics provide a simple and useful characterization of the swing mechanics.
1. A swing quality measurement system comprising:
a memory;
a processor coupled with said memory;
a sensor coupled with said processor and configured to capture a time series of sensor data associated with a bat during a swing of said bat by a user, wherein said sensor comprises one or more of
one or more cameras, wherein said time series of sensor data comprises images or video comprising a time sequence of frames used to generate acceleration data and angular velocity data of said bat,
an inertial sensor that comprises
a three-axis accelerometer that generates acceleration data of said bat, and
a three-axis gyroscope that generates angular velocity data of said bat,
a radar sensor,
a LIDAR sensor,
an ultrasound sensor;
a bat geometry stored in said memory, said bat geometry comprising one or more of
a sweet spot position along a longitudinal axis of said bat, and
a location of a hand position along said longitudinal axis of said bat;
wherein said processor is configured to
receive said time series of sensor data from said sensor,
obtain said bat geometry;
calculate a position and an orientation over time of said bat and of specific points on said bat from said bat geometry;
calculate a trajectory of one or more of said specific points on said bat at points in time through said swing of said bat;
determine a time of impact of said swing from said time series of sensor data;
calculate one or more swing quality metrics comprising one or more of a rotational acceleration metric, an on-plane efficiency metric and a body-bat connection metric,
wherein said calculate said one or more swing quality metrics is based on one or more of
said time series of sensor data;
said position and said orientation over time of said bat and of said specific points on said bat;
said trajectory of said one or more of said specific points on the bat; and,
said time of impact;
wherein
said calculate said position and said orientation over time of said bat and of said specific points on said bat,
said calculate said trajectory of said one or more of said specific points on the bat, and
said determine said time of impact of said swing,
are performed before or during said calculate said one or more swing quality metrics.
2. The swing quality measurement system of claim 1 , wherein
said calculate said trajectory of said one or more of said specific points on the bat comprises
calculate one or more of
a trajectory of said sweet spot position from said time series of sensor data,
a trajectory of said hand position from said time series of sensor data; and
a trajectory of said longitudinal axis from said time series of sensor data.
3. The swing quality measurement system of claim 2 , wherein said processor is further configured to calculate one or more of said one or more swing quality metrics based on at least one or more of said trajectory of said longitudinal axis, said trajectory of said sweet spot position and said trajectory of said hand position.
4. The swing quality measurement system of claim 3 , wherein said processor is further configured to calculate a body tilt axis of said user from said trajectory of said hand position.
5. The swing quality measurement system of claim 4 , wherein said body tilt axis is perpendicular to a plane passing through three different points of said trajectory of said hand position.
6. The swing quality measurement system of claim 4 , wherein said processor is further configured to calculate a time series of body-bat angles, wherein each body-bat angle of said time series of body-bat angles comprises an angle between said longitudinal axis and said body tilt axis.
7. The swing quality measurement system of claim 6 , wherein said processor is further configured to calculate a connection-at-impact metric of said body-bat connection metric of said one or more swing quality metrics comprising said angle at said time of impact.
8. The swing quality measurement system of claim 7 , wherein said processor is further configured to calculate a disconnection-at-impact metric of said body-bat connection metric of said one or more swing quality metrics comprising an absolute value of a difference between said connection-at-impact metric and ninety degrees.
9. The swing quality measurement system of claim 7 , wherein said processor is further configured to
calculate a start time of centripetal acceleration comprising a time during said swing at or near a time when a longitudinal acceleration changes sign, wherein said longitudinal acceleration comprises acceleration of said bat in a direction of said longitudinal axis; and,
calculate a connection-early metric of said one or more swing quality metrics comprising said angle at said start time of centripetal acceleration.
10. The swing quality measurement system of claim 9 , wherein said processor is further configured to calculate a disconnection-early metric of said one or more swing quality metrics comprising an absolute value of a difference between said connection-early metric and ninety degrees.
11. The swing quality measurement system of claim 9 , wherein said processor is further configured to
calculate a disconnection-at-impact metric of said one or more swing quality metrics comprising
an absolute value of a difference between said connection-at-impact metric and ninety degrees;
calculate a disconnection-early metric of said one or more swing quality metrics comprising
an absolute value of a difference between said connection-early metric and ninety degrees; and,
calculate an average-disconnection metric of said one or more swing quality metrics comprising
an average of said disconnection-at-impact metric and said disconnection-early metric.
12. The swing quality measurement system of claim 1 , wherein
said processor is further configured to calculate a swing plane from said time series of sensor data, wherein said swing plane is spanned by a velocity vector of said sweet spot position at said time of impact and said longitudinal axis at said time of impact; and
said calculate said one or more swing quality metrics is further based said swing plane.
13. The swing quality measurement system of claim 1 , wherein said sweet spot position comprises one or more of
an optimum location on said bat for striking a ball;
a position on said bat that maximizes energy transfer when striking said ball;
a position on said bat that maximizes ball speed when striking said ball; and,
a position on said bat that minimizes vibration when striking said ball.
14. The swing quality measurement system of claim 1 , wherein said processor is further configured to
calculate a start time of centripetal acceleration comprising a time during said swing at or near a time when a longitudinal acceleration changes sign, wherein said longitudinal acceleration comprises acceleration of said bat in a direction of said longitudinal axis.
15. The swing quality measurement system of claim 14 , wherein said rotational acceleration metric comprises
a difference between
said longitudinal acceleration at an early rotation time, wherein said early rotation time comprises said start time of said centripetal acceleration plus a fixed offset; and
said longitudinal acceleration at said start time of said centripetal acceleration.
16. The swing quality measurement system of claim 15 , wherein said fixed offset is in a range between 10 milliseconds and 50 milliseconds.
17. The swing quality measurement system of claim 1 , wherein said processor is further configured to
obtain or calculate angular velocity data from said time series of sensor data;
define a swing plane coordinate system comprising
a z-axis along said longitudinal axis;
a y-axis normal to said swing plane; and
an x-axis orthogonal to said y-axis and to said z-axis;
transform said angular velocity data to said swing plane coordinate system, to yield a time series of transformed angular velocities, wherein each transformed angular velocity of said time series of transformed angular velocities comprises a vector sum of
a z-axis angular velocity;
a y-axis angular velocity; and
an x-axis angular velocity;
calculate a time series of rotation-on-plane ratios, each rotation-on-plane ratio of said time series of rotation-on-plane ratios comprising a ratio of
a magnitude of said y-axis angular velocity to
a magnitude of a vector sum of said y-axis angular velocity and said x-axis angular velocity; and,
calculate said on-plane efficiency metric of said one or more swing quality metrics based on said time series of rotation-on-plane ratios.
18. The swing quality measurement system of claim 17 , wherein said processor is further configured to
calculate a start time of centripetal acceleration comprising a time during said swing at or near a time when a longitudinal acceleration changes sign, wherein said longitudinal acceleration comprises acceleration of said bat in a direction of said longitudinal axis; and,
said on-plane efficiency metric comprises
an average of said time series of rotation-on-plane ratios from said start time of said centripetal acceleration to said time of impact.
19. The swing quality measurement system of claim 1 , further comprising
a database of swing quality metrics for a plurality of players; and
an analytics system configured to compare a player or a potential player to said swing quality metrics for said plurality of players.