Measurement of contact time in short duration sports ball impacts: an experimental method and correlation with the perceptions of elite golfers

The perception of ‘feel’ during a ball-implement impact is considered a significant determinant in equipment selection. Previous studies in golf have found that the perceived time for which the ball and clubface are in contact is a factor in the ‘feel’ of the shot. This factor appears to have become more significant with the development of the latest metal ‘woods’. The purpose of this study was to investigate whether golfers’ perceptions of impact duration correspond to measured values or whether the perceptions are created by other factors. A technique has been developed to measure the duration of impact by creating an electrical circuit in which the ball and clubface form a ‘switch’, completing the circuit whilst contact is maintained between the two bodies. Measurements were taken of the duration of impact between five different types of clubhead and two different constructions of golf ball. Further tests, also reported in this paper, investigated the effect of both clubhead speed at impact and ball compression on the impact duration. The results suggest that the ball has a greater effect on impact duration than the type of clubhead with lower compression balls producing longer impact durations than higher compression balls and two piece balls producing shorter impact durations than three piece, wound balls. It was also found that the duration of impact decreased as the clubhead speed at impact was increased. Finally, results suggest that there is no correlation between the perception of the golfer and the actual duration of impact and therefore other factors are responsible for creating this perception

Remote vibration measurements: compensation of waveform distortion due to whole body translations

Remote vibration measurements using the laser Doppler technique are a practical and increasingly popular alternative to the use of contacting transducers. This study concerns aspects of non-contact measurements that result when the vibrating target additionally undergoes larger scale whole body translation. The characteristics of a single remote measurement of steady state vibration on a body undergoing whole body translation are investigated in both the time and frequency domains, where waveform distortion and whole body target displacement induced harmonics are observed. A technique which compensates for the relative whole body displacement between the target and a remote transducer is introduced, in which two simultaneous remote measurements are combined to derive a closer estimate of the measurement which would be made by a contacting transducer attached to the target surface. A substantial improvement in the data quality obtainable from a single remote measurement is demonstrated using a numerical simulation and in experimental data captured remotely from a golf club head during and immediately following an impact with a golf ball. Remote measurements are particularly suited to analysis of impacting bodies and the displacement compensation technique is thus developed in this paper to investigate transient pulse propagation effects. The improvement in data quality obtained is demonstrated using data pertaining to the deformation of a golf ball during an impact in which the whole ball accelerates forwards rapidly

Experimental analysis of impacts with large elastic deformations. Part 1: linear motion

A measurement system is presented which uses a small number of sensors to capture relevant information by a limited number of measurements during a high-speed impact between two lightweight bodies. Two laser Doppler vibrometers and a piezoelectric accelerometer are arranged to capture data from which the variation of deformations, velocities and forces over time during an impact can be determined. The golf club - ball impact is chosen as an example. Large elastic deformations are measured on the golf ball during the impact and these can be related to the variation of the impact force over time. This information leads to greater understanding of the relationship between two impacting bodies and can be used in the validation of analysis by techniques such as finite element modelling

Hollow golf club head modal characteristics: determination and impact applications

The design of modern hollow golf club heads is a labor-intensive process involving extensive performance testing both by robotic and real golfers. This paper describes how, by correlating club head mechanical behavior with functional performance, it will become possible to use validated computational models to predict this performance as well as related contributions to the ill-defined concept of "feel." Successful use of experimental modal analysis to validate a hollow golf club head finite element model is reported. Modal tests employing noncontacting, laser-based transducers facilitated identification of the natural frequencies and corresponding modeshapes for the three main surfaces of the club head. The experimental data suggest predominantly different modal characteristics for each surface, and this compares favorably with equivalent data obtained from the finite element model. The modal data are also used to identify surfaces responsible for particular frequency components present in the club head impact sound spectrum. The potential for detailed impact performance prediction using the finite element model is further demonstrated by comparison of computed and experimental club head acceleration measurements recorded during simulated and actual club-ball impacts

Evaluation of impact sound on the 'feel' of a golf shot

The ‘feel’ of a golf club is an important characteristic that has a significant influence on a golfer's choice of equipment. The sound from impact varies between different clubs and balls and this has been found to contribute to the feel of a shot. The aim of this study was to investigate the relationship between the impact sound and elite golfers’ subjective perceptions of the shot. Suitable test procedures were developed to quantify the golfers’ perceptions using a questionnaire and to measure the impact sound from the same shots. Statistical techniques were then employed to identify correlations between parameters of the impact sound and the golfers’ subjective ratings. The characteristics sharpness and loudness of sound and pleasantness and liveliness of feel were found to be strongly correlated; a shot was rated as having a pleasant feel if it had a loud, sharp sound and a lively feel. Strong positive correlations were also obtained between the subjective ratings and parameters of the impact sound such as sound pressure level, loudness level (according to ISO 532) and sharpness

Experimental studies of the aerodynamics of spinning and stationary footballs

The accurate discrimination of the aerodynamic parameters affecting the flight of sports balls is essential in the product development process. Aerodynamic studies reported to date have been limited, primarily because of the inherent difficulty of making accurate measurements on a moving or spinning ball. Manufacturers therefore generally rely on field trials to determine ball performance, but the approach is time-consuming and subject to considerable variability. The current paper describes the development of a method for mounting stationary and spinning footballs in a wind tunnel to enable accurate force data to be obtained. The technique is applied to a number of footballs with differing constructions and the results reported. Significant differences in performance are noted for both stationary and spinning balls and the importance of the ball orientation to the flow is highlighted. To put the aerodynamic data into context the results are applied in a flight model to predict the potential differences in the behaviour of each ball in the air. The aerodynamic differences are shown to have a considerable effect on the flight path and the effect of orientation is shown to be particularly significant when a ball is rotating slowly. Though the techniques reported here are applied to a football they are equally applicable to other ball types

Evaluation of vibrotactile sensations in the 'feel' of a golf shot

Players’ subjective perceptions of the characteristics, suitability and quality of sports equipment will have a significant bearing on their equipment selection. The ‘feel’ of a golf club is such a perception and the vibration at impact perceived by the player is generally considered to contribute significantly to ‘feel’. The aim of this study was to investigate the correlation between golfers’ subjective perceptions of the feel of a shot and the post-impact vibration of a club. Suitable test procedures were developed to quantify the golfers’ perceptions and to obtain measurements of vibration at the hands. The five feel characteristics investigated, ‘pleasantness’, ‘hardness’, ‘solidity’, ‘liveliness’ and perceived vibration level, were found to be strongly correlated; shots that were regarded as having a pleasant feel were also rated as having felt solid, lively, soft and with little vibration perceived. When these ratings were correlated with raw measurements of impact vibration, the relationships were initially weak. Techniques, such as normalizing the data, weighting the data and using mean data, were developed, resulting in much stronger correlations. Ultimately, a reduction in the total rms vibration level was found to correlate well with the players’ subjective descriptions of ‘pleasant’, ‘solid’, ‘lively’ and ‘soft’ feel

Development and evaluation of new control algorithms for a mechanical golf swing device

Golf swing machines have become fundamental tools in the development of new equipment because they provide more consistent swing motions than golfers. Golf robots perform a simplification of the complex sequence of motions that compose a golf swing; however, traditional devices are typically capable of performing only a single swing profile at variable speeds. Significant differences exist between individual golfers’ swing motions, especially for golfers of different ability, experience, and physical stature, which suggests a requirement for swing profile variability in mechanical simulators. This investigation has found that the swing motion of a traditional golf robot provides a poor representation of golfers’ swings and, as a result, a bespoke control system has been developed for a commercially available golf robot to enable performance of variable swing profiles with positional feedback. Robot swing command files are generated by fitting a curve to a number of discrete data points that are equally spaced in time, and which define angles representative of individual golfers’ swings. The swing profiles of a professional golfer and a traditional golf robot were repeated accurately using this golf robot with a modified motion control system. The capability for individual golfers’ swings to be accurately replicated using a mechanical device was demonstrated using feedback data. All manufacturers recognize the importance of tailoring equipment to the unique characteristics of a particular golfer’s swing, and this increased robot functionality will provide considerable benefits in the development of customized equipment

Human perceptions of sports equipment under playing conditions

Assessment of sports equipment ‘performance’ is generally derived from physical and technical parameters, such as power, speed, distance and accuracy. However, from a psychological perspective, players need to feel comfortable with their equipment and confident in its properties. These factors can only be measured via the subjective assessment of individual perceptions. Using a study of a group of elite golfers as an example, this paper presents a formalised approach for eliciting and structuring player’s descriptions of their perception of sports equipment. Qualitative methods of inquiry are employed to generate perceptions from a group of professional golfers (n=15) during play testing. The equipment characteristics of significance to the golfers emerged from an inductive analysis of their responses. However, whilst this method of representation of the results was invaluable in identifying the key components or dimensions of a player’s sub-jective perception, it was insufficient to describe the potential relationships between the dimensions. With this in mind, a new technique, entitled structured relationship modelling, was developed to illustrate these associations. Ten general dimensions emerged from the analysis, of which three are presented in this paper along with a section of the relationship model. These results demonstrate the effectiveness of qualitative techniques for eliciting human perceptions and of structured relationship models for representation of the associations found

Human perceptions of artificial surfaces for field hockey

Measuring the performance of a sports surface is typically derived from a series of field and laboratory tests that assess the playing properties under simulated game conditions. However, from a player’s perspective their own comfort and confidence in the surface and its playing characteristics are equally if not more important. To date no comparative study to measure playing preference tests has been made. The aim of this research was to develop a suitable method for eliciting player perceptions of field hockey pitches and determine the key themes that players consider when assessing field hockey pitches. To elicit meaningful unbiased human perceptions of a playing surface, an individual subjective analysis was carried out, using interviews and inductive analysis of the recorded player statements. A qualitative analysis of elite hockey players (n = 22) was performed to obtain their perceptions immediately after a competitive match. The significant surface characteristics that emerged as part of an inductive analysis of their responses were grouped together and formed five general themes or dimensions: player performance, playing environment, pitch properties, ball interaction and player interaction. Each dimension was formed from a hierarchy of sub-themes. During the analysis, relationships between the dimensions were identified and a structured relationship model was produced to highlight each relationship. Players’ responses suggested that they perceived differences between pitches and that the majority of players considered a ‘hard’ pitch with a ‘low’ ball bounce facilitating a ‘fast’ game speed was desirable. However, further research is required to understand the relative importance of each theme and to develop appropriate measurement strategies to quantify the relevant engineering properties of pitch materials