This study recorded putter kinematics utilizes ultrasonic sensor and high-speed camera to capture ball roll kinematics parameters, also determine the horizontal ball trajectory.
3.3.1. Putting Performance
The ball roll photos were captured from when the ball moves from its start position to when the ball stop moving—each putt was recorded from the start position to the final stop position. Putting performance is determined as holing percentage (%) based on putts were holed rate.
3.3.2. Putting Kinematics
The three-dimensional putting data were recorded using the ultrasound system Puttlab (Science & Motion Sports GmbH, Flörsheim, Germany). The system was mounted on the putter and calibrated with SAM Station to a secure levelled setup, perfect alignment to the target, and minimum variability of the putting data. A transmitter with three sensors (70Hz *3) was clipped onto the putter shaft. The transmitter was calibrated to the target line using the SAM PuttStation, where the reference frame is the academic centre of the putter face, as illustrated in Fig. (1).
Data collected used SAM Puttlab software which determines with precision to one-tenth of a millimetre for position and one-tenth of a millimetre for alignment (Marquardt, 2007). Evidence to support the reliability of the PuttLab system is provided by previous research (Karlsen et al., 2008a; Toner & Moran, 2011; Wu et al., 2020).
The kinematic 3D data were analyzed by SAM PuttLab 6 software, which included specific algorithms for analyzing human movement data (Marquardt & Mai, 1994). Definition of putter kinematics listed in, listed in Table 3.3.
Table. 3.3.
Definition of putter kinematics parameters.
The x-axis was from the centre of the putter face along the initial direction of the putt and was coincident with the target line. The y-axis extended parallel to the ground away from the golfer. The z-axis extended vertically up from the ground, according to the right-hand-rule.
Putter orientation and plane axis were illustrated in Figure 3.4.
Figure 3.4. Definition of various axis and relation to the target.
The face angle was calculated in the XY-plane, which was perpendicular face angle relative to the target line and recorded at address position and impact with the ball. Putter path was in
Parameters Common Unit Terminology
Clubhead speed m/s, mph Speed of clubhead prior to impact
Attack angle deg Vertical angle of clubhead trajectory Clubhead path
Club direction deg Horizontal angle of clubhead trajectory
Face angle deg Horizontal angle of clubface to target line
Clubhead orientation Dynamic Loft deg Vertical angle of clubface to target line
Dynamic Lie deg Horizontal angle of clubface to ground
Horizontal mm
Vertical mm Vertical distance from center of the clubface of ball impact
Impact location
Horizontal distance from center of the clubface of ball impact
the plane parallel to the ground and defined as the angle between the putter head velocity vector to the target line at impact. The face centre was defined as the geometric centre of the putter head, defined by alignment marking on the putter head and calibrated to the target line. The horizontal spot was the face impact position along the heel-toe axis or y-axis of the putter. The vertical spot was defined as the distance from the putter face centre on the z-axis at impact.
Velocity at impact was defined as the velocity of the putter face centre along the x-axis at the impact position. The rise angle was defined by the angle of the movement of the putter head relative to the z-axis plane at the impact position. The shaft angle was defined as the z-axis or the vertical position of the shaft at impact.
The putting phases were divided into three key phases, backswing phase (address to top-of-backswing), impact phase (top-of-backswing to impact) and follow-through phase (impact to finish) which combines as the downswing phases. Putter kinematics include putter-face angle, putter-path angle, horizontal impact, vertical impact spot, putter-head velocity, rise (attack) angle, and dynamic loft. Rotation to impact was the face angle degree change from top-of-backswing to impact. Definition and terminologies are illustrated in Figure 3.4.
Figure 3.5. Putter kinematics parameters. (a) Face angle measurement convention. (b) Putter path measurement convention. (c) Horizontal and vertical impact spot on the putter-face. (d)
The rise angle and shaft angle at impact measurement convention.
3.3.3. Ball Launch Acquisition
Single high-speed camera (120fps) is used to capture the golf ball parameters from XY-plane 2.5m. The calculation of the ball roll parameters dividing the photograph into x- and y-coordinates. A 1,440 x 860-pixel photograph would consist of 1,440 values along the x-axis and 860 values along the y-axis. The location of the hole and final position can be specified in x, y coordinates. The study uses x, y coordinates and line of putt; trigonometry was applied to calculate ball roll parameters. For distance measurements, the pixels values were converted into centimetres. The above conversion is possible due to the calibration of the system using a scaled mat (four plots of 43x28cm), to calibrate ratio of pixels correspond to the mat. Finally, data is exported and calculate parameters includes the ball initial velocity, ball distance, lateral launch direction, skid distance, skid ratio, roll distance, and roll ratio measured listed in Figure 3.5.
Table. 3.4.
Definition of ball roll kinematics parameters.
The starting position from two-metres, four metres, and hole position is calibrated before each experiment to ensure the position of the camera and lens and illustrated in Figure 3.6.
Parameters Common Unit Terminology
Ball Speed m/s, mph Resultant speed of the ball after impact
Vertical deg Vertical angle of clubhead trajectory Ball path
Horizontal deg Horizontal angle of clubhead trajectory
Skid distance m Distance of ball traveled before rolling
Skid ratio % Percentage of skid over full distance of ball Ball Roll
Roll ratio % Percentage of roll over full distance of ball
Total Distance m Distance of ball total traveled
Smash % Efficiency relationship between ball and clubhead
velocity
Figure 3.6. Experiment setup for Ball Roll Kinematics. (a) Four meters’ starting position. (b) Two-meters starting position. (c) Hole location.