GB2551535A

GB2551535A - A golf swing analyser

Info

Publication number: GB2551535A
Application number: GB1610812.8A
Authority: GB
Inventors: Alexander Borrie John
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-06-21
Filing date: 2016-06-21
Publication date: 2017-12-27
Also published as: GB201610812D0

Abstract

A golf swing analysis system comprising an optical reflector 2 arranged in use on a golf club 3; an optical transmitter 4A, 4B arranged to transmit an optical beam across the swing path of the club; and a corresponding receiver 8A, 8B arranged to detect a reflected beam from the surface of the reflector as it passes through the beam during a swing; characterized in that the system includes a comparator 15A, 15B which compares amplitudes or functions of amplitude of the reflected beams from points or zones on the reflector which are spaced apart in the direction of the swing in order to determine information about the angle of the head of the club. Preferably the plane of the reflector is perpendicular to both the plane of the clubface and the plane of the ground and comprises two diffuse reflective zones 2C, 2D separated by a non-reflective spacer 2E. Also claimed is a measurement unit and method of analysis for the same.

Description

A Golf Swing Analyser

The present invention relates to a golf swing analysis system to assist a golfer with improving the accuracy and consistency of their swing.

Developing a straight consistent swing, with a straight club-head at impact is a major objective for anyone hoping to play golf to a reasonable standard. Once developed, maintaining a good swing requires regular practice.

The present invention was conceived to allow much of this learning and practice to be done without the need to hit a golf ball, and thus take place in locations, such as at home, where it is often impractical to hit golf balls. US4979745 is directed to a system including an active responder or relay recessed into the club-head. Reflected signals from the active responder are detected by two receivers on a ground unit, the difference in amplitude of the relayed signal at the two receivers is used to determine swing angle. The document teaches that small deviations of club-head angle from straight makes negligible difference to the calculation of swing angle and so can be ignored. US4251077 is arranged to provide a focused optical beam directed towards a mirror carried by the club-head. A row of optical detectors is used to determine the direction of the reflected beam. A direction divergent from straight indicates that the swing direction and/or the club-head angle is not straight; however, the system is not able to differentiate between the two. US2006/0014589 is directed to a system that uses two parallel beams generated from a transmitter unit and detected by a separate receiver unit. The golf club-head is swung between the transmitter unit and a detector unit, interrupting the beams, and the timing of these interruptions is used to calculate and display the club-head velocity. US 5257084 relates to a simple system using two infrared beams directed towards the club-head during a swing. The club carries a reflector on its hosel, which is just above the club-head, and the timed reflections from this are used to calculate and display the club-head speed. No attempt is made to assess the swing direction or club-head angle. US6095928 describes a system having three detectors arranged to receive reflected light from a spherical plastic reflector, and to determine the three dimensional path of the club head from identifying angles and changes in the angles of the reflective light received by the detectors. US2002/0103035 relates to an arrangement that floods a detection volume with infrared light, and comprises a series of detectors arranged to detect the passage of a club-head reflector through a set of planes arranged at different angles. The system determines the club-head angle by comparing amplitudes of reflected signal in the detection planes, on the basis that greater amplitude is expected to be received by the detector that is most aligned with the yaw angle of the reflector. The calculations required to interpret the data collected are substantial and the system is complicated to design and manufacture.

According to the invention there is provided a golf swing analysis system comprising: an optical reflector arranged, when in use, on a golf club; an optical transmitter arranged, when the system is in use, to transmit an optical beam across the swing path of the golf club; and a corresponding optical receiver arranged to detect a reflected optical beam from a reflective surface of the optical reflector as a result of the reflector passing through the beam during a swing; characterised in that the golf swing analysis system comprises a comparator that compares amplitudes and/or functions of amplitude of the reflected optical beam as reflected by the optical reflector from points and/or zones of the reflective surface spaced apart in the direction of swing of the club to identify club-head angle information.

This arrangement allows the system to identify whether the front of the reflector, with respect to the direction of swing, passes closer to the receiver than the rear of the reflector. Through knowing the orientation of the reflector surface with respect to the club-head, it is possible to identify club-head angle information, e.g. whether the club-head is straight with respect to the direction of swing or deviated towards an open or closed orientation.

It will be appreciated that the points and/or zones need only be spaced apart in a direction that includes a component that is in the direction of swing, i.e. so that the first point/zone passes through the optical beam before the second point/zone. Expressed another way, the first point/zone of reflection is forward of the second point/zone in the direction of swing.

It is highly preferable that the reflector produces a relatively diffuse reflection. Materials that are highly reflective, i.e. mirror like, are less suitable because the degree of derogation/diffusion of the beams from these materials over the relatively short distance between the golf club swing path and the detectors is so small as to make it difficult to determine a difference in amplitude between the detected reflections.

The desired degree of diffuse reflection may be provided by a light or white coloured, more favourably matt, surface. The inventor has identified that white or light coloured paper/cardboard or similar is particularly suitable though other materials such as, for example, light or white colour synthetic plastics material, or any light or white matt painted surface may be equally effective.

Typically, the reflective surface lies in a plane that passes or is parallel to a plane that passes through a club face of the golf club and a rear of the club-head - the club face being typically the leading face of the golf club-head when swung. As ‘wooden’ club-heads are often rounded, this allows the reflective surface to be conveniently mounted to the club-head in a manner such that when the club-head and swing are straight with respect to the desired direction of swing, the reflective surface will lie in a plane that is perpendicular to the transmitted beam. To achieve this, the reflector preferably includes a body mounted to or near the club-head that carries/defines the reflective surface.

In the preferred arrangement, in which the optical beams are arranged to cross at substantially right angles to a swing path that corresponds with a straight swing, it is preferred that the reflective surface is arranged in a plane lying substantially perpendicular to the club face. Similarly, it is also preferred that the reflective surface is arranged in a plane that, when the reflector passes through the beam, lies substantially perpendicular to the ground.

It is preferred that the reflector is mounted to the head of the golf club. It would be possible, in theory, to attach the reflector to the hosel or shaft of the club; however this is less preferred because it makes it harder to accurately position and maintain the face of the reflector in the required orientation with respect the club-head face.

It is possible that an indication of the club-head angle can be obtained by comparing the amplitudes of reflections from two different points/zones on a single reflective surface, one point/zone being nearer the club face than the other; however it is preferred that the reflector comprises two reflective portions spaced apart in the direction of the swing with a non or relative low reflective portion betwixt. This makes it more straightforward to identify the two reflections to be compared. The two portions could be defined by separate reflective units or by a single reflective member

More preferably, the comparator is arranged to identify and compare maximum amplitudes, or functions thereof, of reflections from the first and second reflective portions This simplifies the method as the derived maximum amplitudes can be determined straightforwardly and provide convenient reference amplitudes representative of the distances of the two reflective points/zones from the receiver.

Favourably the reflector comprises a non-reflective spacer between the reflective portions. This ensures that the amplitude of the reflected beam will significantly decrease between the reflections from the two elements - as compared say with only leaving a gap between the portions which could generate unpredictable background reflections depending on what was behind the reflector - making identification of the relevant reflections more straightforward. This also simplifies construction of the reflector as a single unit making the reflector easier to fit to the club.

It is also preferable that the reflector further comprises non-reflective portions on either sides of the reflective elements. This prevents/reduces the likelihood of detection of spurious reflections e.g. from objects behind the club, or in other words acts to distinguish the beginning and end of reflections derived from the reflector from potential background reflections.

It is preferred that the reflector is passive as this significantly simplifies the design, cost and practicality of the system. The reflector can consequently be made using low cost materials making replacement more readily affordable.

It is preferred that the reflective elements and non-reflective spacer are defined by a printed pattern, favourably onto a light or white surface.

In a preferred embodiment, the system comprises two optical transmitters arranged, when the system is in use, to transmit two optical beams across the swing path of the golf club, the beams being spaced along the swing path of the golf club; and corresponding optical receivers arranged to detect reflected optical beams from the optical reflector when the reflector passes through the beams during a swing. This enables the system to determine swing angle of the club. Because the system identifies two amplitudes as the reflector passes each of the two beams, this allows two calculations to be performed for each of club-head angle and swing direction and these can be compared or checked for consistency.

It would be possible for the system to simply provide the degree of deviation of either club face angle or swing angle from straight; however it is believed that in many cases it is preferable to provide simply an indication that the club-head is straight, open or closed and that the swing is straight, in-out or out-in. In practice, indicating very small deviations from a straight club head angle and a straight swing may be undesirable depending upon the competency or desired competence of the player.

It is preferred that outputs of the comparators indicative of differences in the amplitudes of the reflected beams are compared with predetermined threshold figures. Favourably the thresholds are experimentally determined, as in practice purely mathematically determined thresholds are considered less accurate due to the difficulties in representing real life environment factors associated with a golf club being swung.

Because the relationship of the difference between compared amplitudes (or functions thereof) and the deviations from straight is dependent upon the distance of the reflector from the receiver(s), and because this relationship is not linear, the threshold figures are preferably selected based upon amplitudes of a reflected beam, these being indicative of distances of reflector from the receiver. Any of the amplitudes of any of the reflected beams may be used for this purpose, as the differences in the distance between each of the first and second points/zones of the reflector and the receiver will be small enough that they can be ignored.

It is further preferred that the system comprises means to determine the speed of the club-head as it travels along the swing path. This may be achieved by recording the time it takes for the club-head to pass between the two optical beams.

It is preferred that the system comprises a display to indicate to the user information regarding the orientation of the club-head, preferably also the swing direction and favourably also swing speed.

It is preferred that the reflector comprises a reflector body and a supporting member to support the reflector body on the golf club, the supporting member being attached to the body so as to allow the angle of the reflector body with respect to the golf club to be altered. This allows the angle that the reflective panel extends away from the supporting member to be adjusted during mounting of the reflector to the golf club head to ensure it sits substantially at a right angle to the ground and at a right angle to the club face.

Favourably the optical transmitter is arranged, when the system is in use, to transmit an infra-red or visible light beam across the swing path of the golf club; and the corresponding optical receiver is arranged to detect the reflected infra-red or visible light beam reflected from the optical reflector when the reflector passes through the beam during a swing. Most favourably the beam is an amplitude modulated infrared beam.

The invention will now be described by example with reference to the following figures in which:

Figure 1 is a perspective view of a golf swing analysis system comprising a measurement unit and reflector mounted to a head of a golf club, shown passing the measurement unit;

Figure 2 is a front perspective schematic of the measurement unit;

Figure 3 is a perspective view of the reflector;

Figure 4 is a side view of the reflector mounted to the head of the golf club;

Figures 5A and 5B illustrate blanks of the reflector body and supporting element used to form the reflector;

Figures 6 is a schematic view of the processing functions held within the measurement unit;

Figures 7A, 7B & 7C are graphical representations of demodulated signals derived from reflected beams received by the measurement unit indicative of straight, open and closed club-heads;

Figures 8A, 8B and 8C are graphical representations of pairs of demodulated signals derived from reflected beams received by the measurement unit indicative of straight, out-to-in and in-to-out swings, with a straight club head; and

Figure 9 is a graphic representation of a pair of demodulated signals derived from reflected beams received by the measurement unit indicative of a swing that is out-to-in with an open club-head.

With reference to Figures 1-6 there is shown a measurement unit 1 placed on the ground beyond where a golf ball would normally be with respect to the a golf player, and a reflector 2 mounted on a club-head 3 of a golf club.

The measurement unit 1 comprises first and second infrared (IR) transmitters 4A 4B arranged to transmit two modulated IR beams 5 and 6 across a swing path of the club-head, represented by arrow 7; and corresponding IR receivers 8A 8B arranged to receive reflected beams from the reflector 2 as it passes through the beams 5 and 6. The measurement unit 1 further comprises a display 8, filter/demodulators 11 A, 11B, maxima identifiers 14A 14B, intra-signal comparators 15A 15B, a controller 16, inter-signal comparators 17A 17B and a memory holding at least two lookup tables 18, 19.

The reflector 2 comprises a reflector body 20 that carries a pattern that defines two light or white areas that provide relatively diffuse reflective surfaces 2C, 2D, and relative dark, preferably substantially black, areas that provide a relatively non-reflective spacer element 2E and relatively non-reflective edge portions 2F.

The reflector 2 also comprises a supporting element 21; both the reflector body 20 and supporting element 21 are comprised of relatively stiff white cardboard.

Figures 5A and 5B show the blanks of the reflector body 20 and supporting element 21 before assembly.

The reflector body blank 20 comprises a larger panel 20A and smaller panel 20B conjoined by a fold line 20C. Onto the larger panel 20A is printed a pattern of parallel stripes that includes two white stripes that provide the reflective surfaces 2C, 2D separated by a dark or substantially black stripe that provides a relatively non-reflective spacer 2E. Further, outlying black strips on either side of the white strips define the non-reflective edge portions 2F.

The supporting element 21 comprises three contiguous panels 21A, 21B, 21C joined end to end by fold lines 21D. To assemble, an end panel 21A of the supporting element 21 is adhered to the rear of the larger panel 20A of reflector body 20. The other end panel 21C of the supporting element 21 and the small panel 20B of the body 20 provide supporting surfaces for mounting the reflector, usually with adhesive (e.g. adhesive tape), to the top of the club-head 3. The fold lines 20C and 2 ID allow the angle of the printed face of the larger panel 20A to be adjusted relative to club-head 3.

When correctly orientated, the printed face of the body 20 that carries the reflective pattern, is arranged, when the club head passes through the beams 5, 6 to lie perpendicular to the club face 3A of the club head 3 (see Fig 4) so as to face the receivers 8A, 8B. As such the face also lies substantially perpendicular to the ground G, as the golf club would normally be hitting a ball.

Use of white or light paper provides diffuse reflected beams. Because the beams reflected by each of the reflector elements 2C 2D are diffuse, the amplitudes of the beams received by the receivers 8A, 8B are dependent upon the distance of each reflective surface 2C 2D from each receiver 8A 8B.

With reference to Figure 6, the receivers 8A and 8B each receive a pulse of reflected radiation from the reflector 2 as it passes through the beams 5, 6 transmitted by corresponding transmitters 4A, 4B.

The receivers 8A 8B output respective voltage signals 9, 10 indicative of the received pulses. Demodulation to compensate for transmission modulation is automatically effected by the receivers 8A 8B. Each of the output signals 9, 10 is filtered and further demodulated by respective filter/demodulators 11A 1 IB to remove unwanted features of each signal attributed, for example, to sunlight, noise and unwanted modulation dependent upon the speed of the reflector 2, ergo club-head, through the beams 5, 6.

The cleaned demodulated signals 12, 13 are fed to maxima identifiers 14A 14B that identify the two maximum amplitudes within each of the signals 12, 13 that correspond to reflections from the two reflective surfaces 2C, 2D.

The two maxima detected by the maxima identifiers 14A 14B in each respective signal 12, 13 are passed on to intra-signal comparators 15A 15B that compare the two maxima within the respective signals 12, 13 and output a measure of the difference to a controller 16. From the output of either comparator 15A 15B the controller 16 can identify whether the club-head was straight, open or closed with respect to the swing.

In addition the maxima indentifiers 14A 14B pass the first detected maximum in each signal 12, 13 to a first inter-signal comparator 17A, and the second detected maximum in each signal 12, 13 to a second inter-signal comparator 17B. The intersignal comparators 17A 17B compare the maxima corresponding to the respective signals 12, 13 and output a measures of the differences to the controller 16. From the output of either inter-signal comparator 17A 17B the controller 16 can identify whether the swing was straight, in-out or out-in.

It will be appreciated that the controller 16, when determining whether the swing was straight, in-out or out-in, from the outputs from the inter-signal comparators 17A 17B, will take into account differences in the maxima between signals that inevitably derives from intrinsic differences in electronic components that transmit, receive and process the two different beams. This can be achieved through a tuning/ calibration during manufacture/before first use.

To assist understanding we refer to Figures 7A, 7B & 7C that illustrate an example signal output from filter/demodulators 11A following passage of the golf club through the beam 5. Each signal pulse comprises two maxima. In Figure 7A, these maxima 30A, 30B are of substantially equal amplitude indicating that the two reflective surfaces 2C 2D passed the receiver 8A at the same distance; this corresponds to a straight club-head. In Figure 7B, the first maximum 30C is of larger amplitude indicating that the reflective element 2D nearest the club face passed closer to the receiver 8A than the second reflective element 2C; corresponding to an open club-head. Conversely, in Figure 7C the second maximum is greater, corresponding to a closed club-head.

The relative sizes of the maxima, of a pulses received from the two receivers 8A 8B are expected to be the substantially the same, as it is unlikely that a club-head 3 would veer from open to closed or vice versa; nevertheless, the two outputs can be compared, and where there is disparity, the signal showing the greater difference between the maxima is used.

In contrast, it is expected, that the relative sizes of corresponding maxima between the two received reflected beams may differ. Through identifying this difference it is possible to establish whether the club swing was straight, in-to-out, or out-to-in.

With reference to Figures 8A, 8B, 8C that illustrate, for convenience on a single plot, two pulses that correspond to outputs from each of the filter/demodulators 11A 1 IB following passage of a reflector through both beams 5, 6. As before each pulse comprises two maxima. By comparing the amplitudes of the corresponding maxima from the two pulses, e.g. the first of each pulse or the second of each pulse, it is possible to determine the swing direction. In Fig 8A, the first and second maxima of each pulse are substantially equal indicating that the reflector 2, and thus the club-head 3, passed the first receiver 8A at the same distance as the second receiver 8B, corresponding to a straight swing. In Fig 8B, the maxima of the first pulse are greater than those of the maxima of the second pulse indicating that the club-head passed the first receiver 8A closer than the second receiver 8B corresponding to an out-to-in swing. In Figure 8C the maxima of the second pulse are greater than of the first pulse indicating that the club-head passed closer to the second receiver corresponding to an in-to-out swing. In all cases shown in Figs 8A-8C, the club-head was straight with respect to the swing direction.

In Figure 9, the maxima of the first pulse are greater than the corresponding maxima of the second pulse; this indicates an out-to-in swing. In addition the first maximum of each pulse is greater than the second maximum of each pulse indicating an open club-head.

Simple comparisons of maxima are enough to indicate whether the swing or club-head are straight or turned in a specific direction, and so indications to a user can be based on these comparisons alone. However, in order to determine degree of deviation from straight, it is necessary to indentify an approximate distance of the club-head from each receiver 8A, 8B as it passes through respective beams 5,6. This can be done in a number of ways. The preferred method is to measure the amplitude of one of the maxima from one of the pulses, and determine a corresponding distance from a distance look-up table 18 held in a memory of the measurement unit, in which the figures have been determined experimentally. Alternatively, a formula may be used; however, this is less preferred as it is believed it is difficult to model beam reflections adequately to provide sufficiently accurate results.

In practice there will be inherent tolerances in the system, and in addition for the purpose of game play and the desired competence of the player, a degree of deviation from true straight is usually acceptable. Therefore in order to accommodate this, and to simplify the information provided to the user of the device, the system comprises a grading mechanism.

To this end the controller 16 is arranged to use the distance identified from look-up table 18 and the grade of accuracy selected by the player to identify a threshold figure from one or more threshold look-up tables 19. The output of the comparator 15A is then compared with the selected threshold figure.

If the output of the comparator 15A is above the threshold figure, it is indicative that the deviation is greater than accepted as straight for that grade and the club-head is assessed as being non-straight.

The lookup tables accommodate the fact the degree of difference between the maxima (i.e. the degree of derivation from straight) depends on the absolute distance of the reflector from the receiver.

The system may also be used to determine the speed of the club head. To do this, the controller is arranged to initiate a counter on receiving the first maximum from maxima identifier 14A, which is stopped upon receipt of the first maximum from the second maxima identifier 14B. As the distance between the two receivers is known, it is possible from this information to determine the speed of the club-head 3 between the receivers 8A 8B.

The controller 16 controls display 8 to optionally display information on any, but preferably all of: the angle of the club-head; the speed of the club-head, and the direction of the swing. It would be possible to use alternative or additional means to convey this information to the user, e.g. through audio means.

It is preferred that the pattern of the reflector comprises vertical strips though the nature of pattern can take various forms so long as it includes light and dark areas. The pattern could include other or different geometric or non-geometric shapes.

Although not preferred, it is possible for the reflector to include only a single reflective surface. In such instances, rather than comparing maxima, the measurement unit would be arranged to compare reflections derived from at least two zones of the single reflective surface, preferably separated in a direction that includes a component in the direction of swing of the club.

It will be appreciated that if the system was only intended to indicate club-head angle, only one transmitter/receiver and associated further signal processing functions would be needed.

Claims

1. A golf swing analysis system comprising: an optical reflector arranged, when in use, on a golf club; an optical transmitter arranged, when the system is in use, to transmit an optical beam across the swing path of the golf club; and a corresponding optical receiver arranged to detect a reflected optical beam from a reflective surface of the optical reflector as a result of the reflector passing through the beam during a swing; characterised in that the golf swing analysis system comprises a comparator that compares amplitudes and/or functions of amplitude of the reflected optical beam as reflected by the optical reflector from points and/or zones of the reflective surface spaced apart in the direction of swing of the club to identify club-head angle information.

2. A golf swing analysis system according to claim 1 wherein the reflective surface is arranged in a plane lying substantially perpendicular to the club face.

3. A golf swing analysis system according to claim 1 or 2 wherein, when mounted to the golf club, the reflective surface is arranged in a plane lying substantially perpendicular to the ground when the reflector passes through the beam.

4. A golf swing analysis system according to any claim 1, 2 or 3 wherein the reflector comprises two spaced apart reflective elements that together define, at least in part, the reflective surface, and in which the elements are spaced apart in the direction of swing of the club.

5. A golf swing analysis system according to claim 4 wherein the comparator is arranged to identify and compare maximum amplitudes or functions therof, of reflections from the first and second reflective elements.

6. A golf swing analysis system according to claim 4 or 5 wherein the reflector comprises a non-reflective spacer between the reflective elements.

7. A golf swing analysis swing according to claim 6 wherein the reflector further comprises non-reflective portions on either sides of the reflective elements.

8. A golf swing analysis system according to any previous claim wherein the reflector is passive.

9. A golf swing analysis system according to any previous claim wherein the reflective surface is a light coloured or white surface.

10. A golf swing analysis system according to any previous claim wherein the reflective surface of the reflector is provided by paper/white cardboard.

11. A golf swing analysis system according to any claim 4-10 wherein a printed pattern defines the reflective elements and non-reflective spacer.

12. A golf swing analysis system according to any previous claim wherein an output of the comparator indicative of a difference in the amplitudes and/or functions of the amplitudes of the reflected beam is compared with a predetermined threshold figure.

13. A golf swing analysis system according to claim 12 wherein the threshold figure is selected based upon a maximum amplitude of the reflected beam.

14. A golf swing analysis system according to any previous claim comprising two optical transmitters arranged, when the system is in use, to transmit two optical beams across the swing path of the golf club, the beams being spaced along the swing path of the golf club; and corresponding optical receivers arranged to detect reflected optical beams from the optical reflector when the reflector passes through the beams during a swing.

15. A golf swing analysis system according to claim 14 wherein a further comparator is arranged to compare the amplitudes of the beams reflected from the first transmitted beam and the second transmitted beam to indentify swing angle.

16. A golf swing analysis system according to any previous claim wherein the reflector comprises a reflector body and a supporting member to support the reflector body on the golf club; the supporting member being attached to the body to allow the reflector body to be tilted with respect to the golf club.

17. A golf swing analysis system according to any previous claim wherein the optical transmitter is arranged, when the system is in use, to transmit an infra-red or visible light beam across the swing path of the golf club; and the corresponding optical receiver is arranged to detect the reflected infra-red or visible light beam reflected from the optical reflector when the reflector pass through the beam during a swing.

18. A golf swing analysis system according to any claim 1-16 wherein the optical transmitter is arranged, when the system is in use, to transmit an infra-red beam across the swing path of the golf club; and the corresponding optical receiver is arranged to detect the reflected infra-red beam reflected from the optical reflector when the reflector pass through the beam during a swing.

19. A golf swing analysis system according to any previous claim wherein the reflector is mounted to the golf-club head.

20. A measurement unit comprising: an optical transmitter arranged, when the system is in use, to transmit an optical beam across a swing path of a golf club; a corresponding optical receiver arranged to detect a reflected optical beam from an optical reflector mounted to the golf club as a result of the reflector passing through the beam during a swing; and a comparator that compares amplitudes and/or functions of amplitude of the reflected optical beam as reflected by the optical reflector from points and/or zones of the reflective surface spaced apart in the direction of swing of the club to identify club-head angle information.

21. A method of analysis of a golf swing to determine an indication of club-head angle, the method characterised in comprising: comparing amplitudes of a reflected beam associated with reflections from points and/or zones of a reflective surface mounted to a golf club, the points and/or zones being spaced apart in the direction of swing of the club to identify club-head angle information.

22. A method according to claim 21 comprising using an optical transmitter to transmit an optical beam across the swing path of the golf club; and a corresponding optical receiver arranged to detect a reflected optical beam from the reflective surface of an optical reflector as a result of the reflector passing through the beam during a swing.