Measurement of Angular Motion in Golf Swing by a Local Sensor at the Grip End of a Golf Club

This paper describes a novel method for measuring golf swing angular motion in a global coordinate system using the 3-D acceleration and angular velocity detected by a local motion sensor set at the grip end of a golf club. Optical direct linear transformation (DLT) is the conventional method for measuring sports motion; however, accurate localization of global coordinates and precise setting of infrared high-speed cameras in the test field are essential. Furthermore, infrared reflectors must be attached to the moving object. The system itself and the fine-tuning are expensive, but an accurately set system can provide precise positions for the moving reflectors. It is effective for measuring translational motion but not angular motion that is based on the principles of measurement. The alternative method that is proposed here is easier in terms of setting and fine-tuning, more reasonable in cost, and more accurate in measuring rotational motion compared with the DLT method. Furthermore, the system's wireless transmitter enables noninvasive measurement. When addressing the golf club, its initial angles and posture matrix are calculated using the 3-D acceleration; when the swing begins, the motion sensor measures the changing angular velocity and the acceleration. The application of step-by-step Euler transformation for each sampling interval yields the angular velocity and angle in the global coordinate system. The mean RMSE of ten trials with five subjects was 3.06°, 26.64°, and 4.43° for the 3-D angle of the club shaft.