Swing measurement device, swing measurement method, and swing measurement program

1. A swing measurement system for measuring an evaluation index of a swing of a golf club using an inertial sensor, the swing measurement system comprising:

the inertial sensor attached to the golf club at an attachment position determined by a measurer, the inertial sensor having a rectangular shape with a length axis, a depth axis, and a width axis, wherein the length axis is aligned with an axial direction of the golf club and the depth axis is aligned parallel to a face surface of the golf club;

a movement trajectory calculation unit that calculates a movement trajectory of the golf club during the swing using a detection value of the inertial sensor at the attachment position;

a shaft plane calculation unit that calculates a shaft plane in the swing based on the movement trajectory in a freely selectable section during the swing; and

an angle calculation unit that calculates a shaft plane angle formed by the face surface of the golf club with respect to the shaft plane as the evaluation index.

2. The swing measurement system according to claim 1 , wherein the shaft plane calculation unit calculates the shaft plane based on the movement trajectory in a freely selectable section from an address position to an apex position of the swing, the apex position being a point at which a head of the golf club has reached a highest position during a back swing.

3. The swing measurement system according to claim 2 , wherein the shaft plane calculation unit calculates the shaft plane based on the movement trajectory from a halfway back position to the apex position during the back swing.

4. The swing measurement system according to claim 2 , wherein the shaft plane calculation unit calculates the shaft plane based on the movement trajectory from the address position to a halfway back position during the back swing.

5. The swing measurement system according to claim 1 , wherein:

the attachment position of the inertial sensor is between a grip of the golf club and a head of the golf club; and

the inertial sensor is a singular unit and is an only inertial sensor attached to the golf club.

6. A swing measurement method for measuring an evaluation index of a swing of a golf club using an inertial sensor, the swing measurement method comprising the steps of:

attaching the inertial sensor to the golf club at an attachment position determined by a measurer, the inertial sensor having a rectangular shape with a length axis, a depth axis, and a width axis;

aligning the length axis of the inertial sensor with an axial direction of the golf club;

aligning the depth axis of the inertial sensor parallel to a face surface of the golf club; and

inputting the attachment position into a computer for use in calculating:

movement trajectory calculating of calculating a movement trajectory the golf club during the swing using a detection value of the inertial sensor;

shaft plane calculating of calculating a shaft plane in the swing based on the movement trajectory in a freely selectable section during the swing; and

angle calculating of calculating a shaft plane angle formed by the face surface of the golf club with respect to the shaft plane as the evaluation index.

7. The swing measurement method according to claim 6 , wherein in the shaft plane calculating, the shaft plane is calculated based on the movement trajectory in a freely selectable section from an address position to an apex position of the swing, the apex position being a point at which a head of the golf club has reached a highest position during a back swing.

8. The swing measurement method according to claim 7 , wherein in the shaft plane calculating, the shaft plane is calculated based on the movement trajectory from a halfway back position to the apex position during the back swing.

9. The swing measurement method according to claim 7 , wherein in the shaft plane calculating, the shaft plane is calculated based on the movement trajectory from the address position to a halfway back position during the back swing.

10. The swing measurement method according to claim 7 , wherein:

the attachment position of the inertial sensor is between a grip of the golf club and a head of the golf club; and

the inertial sensor is a singular unit and is an only inertial sensor attached to the golf club.

11. A swing measurement program configured to cause a computer to execute the calculating in the swing measurement method described in claim 6 .