PMC

Recording and analysis window of a single swing. Swing recording time is 3 s with the impact point set at 2 s. The analysis window has the width of 1.5 s.

Field test. The movement of the golf club during a typical golf swing is recorded by the SG sensors and the IMU device. (a) SG sensors are connected by wire to the nearby cRIO device. (b) The IMU device is connected wirelessly to the nearby laptop (not shown in pictures).

Front SG sensor calibration and validation. The bend is measured directly by the QTM system and indirectly by the SG sensor. The horizontal axis shows the mass of the applied weight in [g], the vertical axis shows the bend of the club head in [mm].

Bending test for SG sensor calibration and validation. The golf club shaft bends under the force exerted to the bottom of the shaft. Bending is calculated from the height difference of two markers measured by the QTM system.

Simplified architecture of IoT sport applications using smart sport equipment and wearables with integrated sensors. Smart sport equipment and wearables send sensor data to the IoT cloud directly or through the gateway. Sensor data processing can be performed locally by the mobile device or in the cloud. Results can be checked by any connected device.

Player’s signatures shown in 2D strain plot indicate that each player has a very distinctive sensor response. Graph (a) shows signatures of experienced amateur players; graph (b) shows signatures of two two professional golf players. The strain in both axes is given in [mε]. The horizontal axis shows the strain of the front sensor and the vertical axis shows the strain of the side sensor.

Player’s signatures of five successful consecutive swings of four different golf players: graphs (a,b) show swings of two experienced amateur players; graphs (c,d) show swings of two professional golf players. All graphs show the response of two orthogonally placed SG sensors, where blue plots represent the front sensor and red plots represent the side sensor. Signals show that each player has a distinctive sensor response (signature).

Smart golf club equipped with various sensors fixed to the shaft at different positions: the IMU device with 3-axis accelerometer and 3-axis gyroscope is just below the grip; two SG sensors pasted orthogonally to each other along the shaft’s axis; Two independent rigid bodies used by the QTM optical system are fixed at the top and at the bottom of the shaft.

Graphical representation of the smart golf club shaft with two orthogonally placed strain gage sensors measuring the bends of the shaft in two orthogonal directions. The front SG senor is placed in the direction of the Z axis and side SG sensor in the direction of the X axis of the Shimmer 3 IMU device; both measured from the axis of the shaft.

Measurement repeatability test. Graphs show sensor signals for the same series of five consecutive swings performed by a professional golf player: (a) two orthogonal SG sensors; (b) 3-axis accelerometer; (c) 3-axis gyroscope. In graph (a) blue plots represent the front sensor and red plots represent the side sensor, while graphs (b,c) red, green, and blue lines represent X, Y, and Z axis respectively.

Comparison of 2D strain [mε] plot for regular swings and swings with technical errors of two professional golf players: (a) Player 1; (b) Player 4. Regular swings (straight) differ from swings with technical errors (slice, draw) in one or more swing phases. We expect the identification of technical errors is possible. The strain in both axes is given in [mε]. The horizontal axis shows the strain of the front sensor and the vertical axis shows the strain of the side sensor.

3D rigid body tracking with Qualisys™ Track Manager. The positions of two independent rigid bodies attached to the golf club shaft at one point in time are shown in the global coordinate system XYZ. Each rigid body is composed of three markers and has an independent local coordinate system with the origin in one of the markers.

Technical error detection. Averages of five consecutive swings: (a) two orthogonal strain gage sensors; (b) 3-axis accelerometer; (c) 3-axis gyroscope. Solid lines represent averages of five consecutive successful swings; dashed lines represent averages of five swings with “slice” technical error. Traces of the same color are distinctively different from each other. We expect that technical error detection is possible. In graph (a) blue plots represent the front sensor and red plots represent the side sensor, while graphs (b,c) red, green, and blue lines represent X, Y, and Z axis respectively.