Swing analysis system that calculates a rotational profile
A system that measures a swing of equipment (such as a bat or golf club) with inertial sensors, and analyzes sensor data to create a rotational profile. Swing analysis may use a two-lever model, with a body lever from the center of rotation to the hands, and an equipment lever from the hands to the sweet spot of the equipment. The rotational profile may include graphs of rates of change of the angle of the body lever and of the relative angle between the body lever and the equipment lever, and a graph of the centripetal acceleration of the equipment. These three graphs may provide insight into players' relative performance. The timing and sequencing of swing stages may be analyzed by partitioning the swing into four phases: load, accelerate, peak, and transfer. Swing metrics may be calculated from the centripetal acceleration curve and the equipment/body rotation rate curves.
1. A swing analysis system that calculates a rotational profile, comprising:
an inertial sensor comprising
an accelerometer;
a gyroscope; and
a network interface;
wherein
said inertial sensor is coupled to equipment;
said equipment is associated with a longitudinal axis;
said equipment comprises
a hand position; and
a sweet spot position;
said inertial sensor is configured to capture inertial sensor data at a sequence of times during a swing of said equipment by a user;
a processor coupled to said inertial sensor via a network connection, wherein said processor is configured to
receive said inertial sensor data; and
based on said inertial sensor data, calculate
a trajectory of said equipment comprising
said hand position at said sequence of times; and
said sweet spot position at said sequence of times;
a center of rotation of said swing;
a body lever at said sequence of times that extends from said center of rotation to said hand position;
an equipment lever at said sequence of times that extends from said hand position to said sweet spot position;
a body rotation angle at said sequence of times, comprising an angle between said equipment lever and a starting equipment lever at a start of said swing;
a hinge angle at said sequence of times, comprising an angle between said equipment lever and a tangent perpendicular to said body lever;
a body rotation rate at said sequence of times, comprising a rate of change of said body rotation angle;
an equipment rotation rate at said sequence of times, comprising a rate of change of said hinge angle;
a centripetal acceleration of said equipment along said longitudinal axis at said sequence of times; and,
a rotational profile comprising
said body rotation rate at said sequence of times;
said equipment rotation rate at said sequence of times; and,
said centripetal acceleration at said sequence of times.
2. The swing analysis system of claim 1 , wherein said equipment comprises a bat.
3. The swing analysis system of claim 1 , wherein said equipment comprises a golf club.
4. The swing analysis system of claim 1 , further comprising
a database comprising
said rotational profile associated with each user of a plurality of users, wherein said plurality of users comprises said user; and,
wherein said swing analysis system with said database is configured to compare said rotational profile across said plurality of users.
5. The swing analysis system of claim 4 , wherein said swing analysis system is further configured to generate recommended equipment for said user.
6. The swing analysis system of claim 5 , wherein said generate said recommended equipment for said user comprises
calculate one or more swing metrics for swings by said user of a plurality of equipment options;
calculate a score for each equipment option of said plurality of equipment options from said one or more swing metrics; and,
identify said recommended equipment as an equipment option of said plurality of equipment options with a highest value of said score.
7. The swing analysis system of claim 6 , wherein said one or more swing metrics comprise
an equipment swing speed at impact; and,
a swing time to contact.
8. The swing analysis system of claim 7 , wherein said one or more swing metrics further comprise one or more addition metrics calculated from said rotational profile.
9. The swing analysis system of claim 1 , wherein said processor is further configured to
partition said sequence of times into phases, wherein said phases comprise
a load phase ending when said centripetal acceleration changes from positive to negative;
an accelerate phase following said load phase;
a peak phase following said accelerate phase; and,
a transfer phase following said peak phase and ending at an end of said swing when said equipment impacts a ball.
10. The swing analysis system of claim 9 , wherein said rotational profile further comprises one or more swing metrics calculated from one or more of
said inertial sensor data;
said body rotation rate at said sequence of times;
said equipment rotation rate at said sequence of times; and,
said centripetal acceleration at said sequence of times.
11. The swing analysis system of claim 10 , wherein said one or more swing metrics comprise
a peak loading acceleration, comprising a maximum positive centripetal acceleration during said load phase.
12. The swing analysis system of claim 10 , wherein said one or more swing metrics comprise
a rate of acceleration, said rate of acceleration comprising an average rate of change of said centripetal acceleration during said accelerate phase.
13. The swing analysis system of claim 10 , wherein said one or more swing metrics comprise
a peak acceleration, said peak acceleration comprising a minimum negative centripetal acceleration after said load phase and before said end of said swing.
14. The swing analysis system of claim 10 , wherein said one or more swing metrics comprise
an acceleration impulse, said acceleration impulse comprising an integral of said centripetal acceleration between a start of said accelerate phase and said end of said swing.
15. The swing analysis system of claim 10 , wherein said one or more swing metrics comprise a time to peak force, said time to peak force comprising a time difference between a start of said accelerate phase and a time when said centripetal acceleration reaches a minimum negative value after said start of said accelerate phase.
16. The swing analysis system of claim 10 , wherein said one or more swing metrics comprise
a peak equipment rotation rate, said peak equipment rotation rate comprising a maximum value of said equipment rotation rate between a start of said load phase and said end of said swing; and,
a peak body rotation rate, said peak body rotation rate comprising a maximum value of said body rotation rate between a start of said load phase and said end of said swing.
17. The swing analysis system of claim 16 , wherein said one or more swing metrics further comprise a ratio between said peak equipment rotation rate and said peak body rotation rate.
18. The swing analysis system of claim 10 , wherein said one or more swing metrics comprise
a peak loading acceleration, said peak loading acceleration comprising a maximum positive centripetal acceleration during said load phase;
a rate of acceleration, said rate of acceleration comprising an average rate of change of said centripetal acceleration during said accelerate phase;
a peak acceleration, said peak acceleration comprising a minimum negative centripetal acceleration after said load phase and before said end of said swing;
an acceleration impulse, said acceleration impulse comprising an integral of said centripetal acceleration between a start of said accelerate phase and said end of said swing;
a time to peak force, said time to peak force comprising a time difference between a start of said accelerate phase and a time when said centripetal acceleration reaches a minimum negative value after said start of said accelerate phase;
a peak equipment rotation rate, said peak equipment rotation rate comprising a maximum value of said equipment rotation rate between a start of said load phase and said end of said swing;
a peak body rotation rate, said peak body rotation rate comprising a maximum value of said body rotation rate between a start of said load phase and said end of said swing; and,
a ratio between said peak equipment rotation rate and said peak body rotation rate.