WO1998018010A1

WO1998018010A1 - Apparatus for measuring parameters relating to the trajectory and/or motion of a moving article

Info

Publication number: WO1998018010A1
Application number: PCT/GB1997/002873
Authority: WO
Inventors: Norman Matheson Lindsay
Original assignee: Norman Matheson Lindsay
Priority date: 1996-10-19
Filing date: 1997-10-17
Publication date: 1998-04-30
Also published as: GB9908258D0; GB2334781B; JP2001502428A; GB2334781A

Abstract

The apparatus comprises one or more light sources (18; 15) for providing light emitted from or reflected by the moving article and one or more light sensing means (15; 12, 50, 51) arranged to provide a signal when illuminated by said light, at least one of the light sensing means (15; 12, 50, 51) being arranged to detect when the moving article intercepts a known detection plane (19, 20, 21, 64, 65, 66, 67), wherever the article intercepts the plane. The sensing means may comprise a slit aperture (10, 11, 12, 23, 60, 61) and/or cylindrical lens to define a detection plane. The apparatus may be used to measure the pre-impact and post-impact position and/or motion of a golf clubhead (7) and/or of a golf ball (1) during execution of a golf shot.

Description

APPARATUS FOR MEASURING PARAMETERS RELATING TO THE TRAJECTORY AND/OR MOTION OF A MOVING

ARTICLE TECHNICAL FIELD

This invention relates to apparatus for measuring parameters relating to the trajectory and/or motion of a moving article and in particular, apparatus for measuring and recording the pre-impact and post-impact position and/or motion of a golf clubhead and golf ball during the execution of a golf shot

BACKGROUND ART

Most contemporary commercial golf swing analysers use arrays of light beams and coacting electro-optical sensors In a typical conventional golf swing analyser a plurality of discrete light sensors are arranged in line at regular known intervals with two or more such arrays built into a playing mat and extending transversely to the intended direction of clubhead travel prior to ball impact The light sensors are normally illuminated from a single source at ceiling height so that the effective light beams received by each sensor in an array are approximately parallel and vertical The light sensors detect the shadow of a clubhead as it travels at speed towards a golf ball By recording and processing the sequence of light interrupts in the light sensors various parameters such as clubhead speed swingpath angle, impact offset and clubface angle at impact can be computed

The clubhead sensing method as outlined above has been established practice for many years US Patent 3,601 ,408 issued in 1971 is one early prior art document which still forms the basis of many of today's golf swing analysers Other prior art in golf swing analysers teaches the use of electro-optical sensors that operate from incident light reflected off part of a clubhead (as distinct from a clubhead interrupting or shadowing directly incident light) This later mode of operation is exemplified in GB 21 15704 and US 5257084

In comparison to known methods the present invention aims to provide more extensive and more precise data using only a relatively small number of sensor signals

According to a first aspect of the invention there is provided apparatus for measuring parameters relating to the trajectory and/or motion of a moving article the apparatus comprising one or more light sources for providing light emitted from or reflected by the moving article and one or more light sensing means each arranged to provide a signal when the respective sensing means is illuminated by said light, wherein at least one of the light sensing means is arranged to detect when the moving article intercepts a given detection plane wherever the article intercepts the detection plane, the arrangement being such that the position and orientation of the detection plane relative to a reference point is known or can be deduced from the signal provided by the said at least one sensing means

According to another aspect of the invention, the apparatus is provided in combination with one or more articles the movement of which is to be sensed, the or each of the articles being provided with a reflective portion and/or light emitting means

The article may comprise a golf club and according to a further aspect of the invention there is provided a golf club for use with the apparatus, the golf club being provided with at least one diffusely reflective region surrounded by a relatively non-reflective region and/or with at least one light emitting means together with a power source therefor During the pre-impact measurement phase the position of a golf ball is fixed (motionless) relative to the apparatus and normally only measurements of the golf clubhead are performed During the post-impact measurement phase only measurements of the golf ball motion are normally required but measurements of the post-impact motion of the clubhead can also be obtained to yield additional information on the impact event

Apparatus according to the invention may be used to provide fast quantitative measurements of various parameters of a golf shot and is of benefit to golfers in providing feedback relating to important aspects of their shot making skills The apparatus is also useful for purposes of custom club fitting, where measurable parameters of a golfer's swing are used in a decision process to select the properties of various components that comprise a golf club The invention may also be used in golf simulation equipment where it is required to compute the hypothetical free flight of a golf ball off a golf shot in confined, flight restricting environments

The purpose of performing measurements on both the clubhead and the golf ball is to obtain data that could not easily be obtained by measuring only the clubhead or only the golf ball

For example in golf simulation applications, it is required to predict the flight of a golf ball from data of its initial launch conditions Whereas some of this data is most easily and reliably obtained from direct measurements of the golf ball after impact other data is best obtained indirectly from measurements of the clubhead prior to impact, and from knowledge of the relevant mass and inertial properties of the clubhead and ball Data that are preferably measured directly are the linear velocity components of the ball Data that are preferably found indirectly from measurements of both the clubhead and the ball are the spin components of the ball The spin components imparted to the ball at impact strongly influence the ultimate distance and direction of flight, but the spin of the ball is very difficult to detect by direct measurement of the ball just after impact Spin is imparted to the ball when the striking surface of the clubhead is oblique to the direction of the line of impact and/or when the centre of mass of the clubhead is off-set from the line of impact For example, if the swingpath angle (i e the azimuth angle of the clubhead motion) and the ball launch angle (in azimuth) are equal, and the impact point is on the ' sweet spot" of the clubhead (nearest to the centre of mass of the clubhead), then the sidespin component of the ball in flight is zero By measuring the clubhead swingpath at impact, the offset of the clubhead relative to the ball at impact and the azimuth launch direction of the ball, an accurate estimate of the magnitude and sense of sidespin imparted to a ball may be made

In club fitting applications, it is desirable to have comprehensive data relating to a customer s golf swing This includes all the components of motion of the clubhead at impact (speed, swingpath angle, attack angle and clubhead rotation), and all the components of the clubhead orientation and position at impact (clubface angle, dynamic e dynamic loft, height and impact offset) In a typical embodiment of a measurement system according to the invention, most of the above parameters can be readily found by direct measurements on the clubhead but others are preferably found by also measuring the direction of the ball as it leaves the clubhead For example the dynamic loft of a clubhead at impact can be determined from measurements of the clubhead attack angle (that is the elevation angle of the clubhead motion at impact), the elevation launch angle of the golf ball and knowledge of the golf ball and clubhead impact characteristics

When the ball is struck, it initially remains in contact with the clubface and travels a distance of a few millimetres before parting from the club Thereafter, the ball travels through the air in a direction that is primarily determined by the pointing direction of the clubface at initial impact and by the direction of motion of the clubhead at initial impact As it travels through the air, the ball is subject to gravity and to various aerodynamic forces but in the first few metres of flight the combination of all these forces has very little effect on the direction of travel, so the initial flight path can be considered to be straight to within a very small fraction of a degree for all normal full swing golf shots

In contrast to the ball motion, the motion of the clubhead is not rectilinear Prior to impact the clubhead moves in a curvilinear arc and is subject to significant rotation about the shaft axis The curvature and plane of the clubhead arc differ from player to player as does the rate of clubhead rotation This curvature of the clubhead motion leads to significant measurement errors in known apparatus where typically swingpath angles are measured at only two points along a substantial portion of a clubhead path prior to impact

In order to equate pre-impact and post-impact events during a golf shot, apparatus according to the invention is preferably capable of predicting the motion of the clubhead very near the point of impact and be capable of resolving small angular differences (e g ±0 5° or better) between the immediate pre-impact motion of a clubhead and the ensuing flight of a ball struck by said clubhead Many known apparatus in common use provide only relatively coarse resolution (typically l 0° for swingpath angle) and are capable of only two dimensional measurements of horizontal components of motion and orientation Thus important parameters such as attack angle, dynamic loft and dynamic lie are absent

Preferred embodiments of the present invention provide equipment which measures clubhead and ball behaviour in the impact region using arrays of electro-optical sensors in conjunction with light aperturing and/or light focusing devices in configurations that provide high quality measurements of all parameters relating to the dynamics of a clubhead-oπ-ball impact and more extensive and more precise data is provided using only a relatively small number of sensors Advantageously, apparatus according to the invention may be used with any standard make of golf club or golf ball and the playing surface or tee-off arrangement can be of unrestricted form as these do not need to form part of the measurement equipment

In a preferred embodiment of the present invention one or more parts of a clubhead are selectively illuminated as the clubhead travels through a region just prior to impact with a golf ball Additionally, one side of the said golf ball is selectively illuminated during part of its initial flight trajectory after impact For convenience the above selectively illuminated parts of a clubhead cr ball are hereinafter referred to as highlights Light emitted from each highlight is detected by a plurality of electro-optical sensor devices arranged in sensor arrays with at least one array configured to detect clubhead highlights and a separate array configured to detect the ball Associated with each sensor device in an array there is provided at least one aperture and/or lens that limits or focuses the field of view of the light sensor device The combination of a sensor device with an aperture and/or focusing lens is arranged to provide a wide angle of view in one plane with a narrow angle of view in the orthogonal plane For convenience we refer herein to the field of view as a 'detection plane'

The wide angle of view of the detection plane preferably extends over at least 5 degrees and in some cases, may extend over at least 120 degrees The narrow angle of view in the orthogonal direction, which determines the thickness of the detection plane preferably extends over 1 degree or less or more preferably over 0 25 degree or less In a typical case, with a divergence of 0 25 degrees and a highlight at a distance of 36 cm from the light sensor the thickness of the detection plane at the point the highlight passes through it will thus be less than 2 mm The detection planes are preferably arranged to traverse the path of a clubhead or ball at various positions along the path and at various angles thereto As a highlight travels into the field of view of a sensor, data capture circuits record the time and amplitude response of the sensor to the received incident light These data are used to compute the speed position and direction of the highlights and thus the clubhead and ball motion

At least one of either a sensing device or a coacting combination of aperture and/or lens is preferably elongate In one form of the invention the said sensor devices comprise discrete sensors (i e having one signal responsive to light incident on one small photo-sensitive area) and the said apertures and/or lenses comprise slit apertures and/or cylindrical lenses In another form of the invention, the sensor devices are elongate and may comprise a linear pixel array (e g a CCD array) or an electro-optical one dimensional position sensitive detector (PSD), whereas the apertures are 'pin-hole types (i e small, circular apertures or the like) and the lenses are spherical, focusing to a point In the case of the linear pixel array, the field of view is composed of a set of overlapping narrow conical beams spread across the detection plane and the linear pixel array is used as a form of position sensitive detector

Both the sensing device and the coacting combination of aperture and/or lens may also be elongate When two such elements are combined (e g a slit aperture coacting with a linear CCD array), a set of detection planes are provided corresponding to each of the pixels in the CCD array When the slit aperture and the CCD array are parallel the above set of detection planes are co-planar and overlapping, but offset slightly from each other When the slit aperture and coacting CCD array are not parallel, then the set of detection planes do not overlap

Typically, the highlights are provided by direct light emission from specially mounted light emitting devices on a clubhead (primary highlights) or by reflection from diffusely reflecting zones (secondary highlights) provided on the clubhead or ball using fixed position primary light emitting arrays to illuminate the reflective zones For practical reasons the highlight from a golf ball is preferably of the latter (secondary) type, and the reflecting zone comprises the hemispherical surface on an illuminated side of said ball

The light emission from a highlight may be continuous or pulsed In one preferred embodiment, low duty cycle pulsed emissions with a repetition frequency in the range 10kHz to 100kHz are used with measurements coinciding with each pulse This corresponds to providing measurements of a clubhead and ball positions at intervals of a few millimetres to a fraction of a millimetre (In a 'full swing' golf shot the clubhead speed at impact is typically in the range 25m/s to 55m/s, and ball launch speeds are typically 30% to 60% greater)

In one embodiment of the invention, highlights for a clubhead are provided as light emitting devices (LED's) which are mounted at known positions on the clubhead (typically near the heel and near the toe) Preferably, the LED's are mounted on a small circuit substrate that is detachable from the clubhead and this substrate contains a suitable compact battery power source and means for controlling light emission and power drain A suitable controlling means comprises a light detector and timing circuitry that are also mounted on the circuit substrate The detector converts incident light from an external controlling light source into a signal that enables an on-board timer and this, in turn, powers the LED's for a predetermined period and also allows time multiplexing of highlights when two or more are provided on a clubhead In this manner the average power consumed by the LED's can be significantly limited by being switched on for only a few milliseconds during each swing Preferably, the LED's and light detector operate in the near infra red (IR) spectrum but visible light or other light wavelengths may be used Using IR wavelengths allows the clubhead mounted assembly to be covered with an overall IR transparent filter that appears to the human eye as an opaque black material Thus the circuit substrate and all on-board components can be hidden so the assembly can be designed to blend in with the clubhead appearance

In a further embodiment, highlights for a clubhead are provided as diffusely reflective zones on one or more known positions on the clubface surface Preferably, the highlights reflect light uniformly across the area of the reflective zone The reflective zones may be circular, but advantageously the zones are specially shaped to enhance the time varying amplitude response of the received sensor signals and to provide features that indicate the orientation and/or position of the highlight relative to a detection plane

One or more primary light sources are preferably provided adjacent to the clubhead-on-ball impact zone and positioned to efficiently illuminate the diffusely reflective zones as the clubhead approaches the ball resting position, but also positioned a safe distance e g at least 20 cm away from possible contact by a clubhead during a normal golf shot An associated sensor array is configured to accept light from such a highlight and means are preferably provided to substantially exclude from the collective field of view of the sensor array, reflected light from other parts of the clubhead and also from background reflections Typically, the clubhead surface closely adjacent to a highlight is provided with a non-reflective coating Other parts of the clubhead surface can advantageously comprise polished or mirror-like reflecting surfaces, providing that such surfaces reflect the primary light source in directions other than into the collective field of view of the sensor array, taking account of the directional characteristics of the primary light source These features ensure that the highlights are well defined and contrast strongly against background light sources during the measurement phase The invention will now be further described, merely by way of example with reference to the accompanying drawings in which

Figure 1 is a schematic diagram in plan view of a clubhead a golf ball and apparatus according to one embodiment of the invention at an instant of a swing just prior to impact,

Figure 2 shows a rear end view of the arrangement in Figure 1

Figure 3 shows a side view of the arrangement in Figure 1 at an instant of a swing following impact,

Figures 4A and 4B show details and views of two types of clubhead adapted for use with the invention,

Figure 5 is a schematic diagram of an arrangement of detection planes for measuring the initial launch trajectory of a golf ball,

Figure 6 shows time dependent waveforms of typical signals that are generated by the arrangement of Figure 5,

Figure 7 shows a scale drawing in plan view of preferred additional mechanical details of the arrangement of Figure 1 ,

Figure 8 shows a front view of the arrangement of Figure 7,

Figure 9 is a schematic diagram of an arrangement of discrete sensors and slit aperture to provide two coplanar detection planes, according to another embodiment of the invention, Figure 10 shows time dependent waveforms typical of signals that are generated in the arrangement of Figure 9

Figure 11 is a diagrammatic plan view illustrating the combination of a PSD device and a slit aperture used in further embodiment of the invention, and

Figure 12 is a diagrammatic side view of the arrangement shown in Figure 11

For convenience, reference axes X Y and Z are shown in the drawings The Z axis is vertical and points upwards The Y axis is horizontal and points along the general azimuth direction of ball travel The X axis is orthogonal to Y and Z and points in the general 'heel-to-toe' direction of a clubhead at ball address

Referring to Figure 1 , a golf ball 1 rests on a rubber tee 2 (shown by dotted circle) The tee 2 is semi-permanently fixed to a playing surface or play-off mat 3 Other ball placement arrangements may be adopted, for example the ball can be placed directly on a mat or on turf provided that the placement spot is nominally on a known vertical axis in relation to the apparatus An IR transmitting and receiving (TX/RX) assembly 4 is provided in a known position and orientation relative to the resting position of the golf ball 1 A signal and power cable 5 connects the TX/RX assembly 4 to signal control, data capture and display unit 6 which can be implemented either as a dedicated control and display module or (via suitable interfacing) as a general purpose stand-alone computer such as a 'PC system

IR emitters 25 (see Fig 3) on the TX RX assembly emit a beam or beams of IR light towards the toe end of a clubhead 7 The IR emission is preferably pulse modulated with a repetition frequency of the order of 50kHz or higher so that ac coupled signal amplification can be applied thus rejecting low frequency background light interference Some of the pulse modulated light is reflected back towards the TX/RX assembly where it passes through a series of slit apertures 23 60 61 (see Fig 3) provided on the front face 8 of the TX RX assembly In particular, light reflects off a specially designed diffusely reflecting zone provided on the toe end 9 of the clubhead Light from this diffusely reflecting zone is intended to be the dominant component of back reflected light from the clubhead This dominant reflecting zone is referred to herein as a highlight

As the highlight passes across the field of view of a sensor inside the TX RX assembly a signal proportional to the instantaneous quantity of light incident on the sensor is generated and stored as data Analysis of the data allows accurate estimation of the instant in time when the centre of the highlight was positioned along the major plane of the field of view of a given sensor For convenience, such a plane is referred to hereinafter as a detection plane Knowing the relative positions and angles of all the detection planes, parameters such as the clubhead speed and swingpath angle can be found from analysis of the highlight time and position data

Referring now to Figures 1 and 3, a second IR TX/RX assembly is provided comprising a TX array 14 and RX array 15 with corresponding signal and power cables 16 17 for connection to the data capture and display unit 6 The TX and RX arrays are shown for clarity as separate units, but in practice these would advantageously be combined into a single assembly The TX array comprises a number of small area IR emitters 18 mounted at approximately equal spacing along a line parallel to the X axis The direction of peak emission for all the IR emitters 18 is typically vertically upward and the individual beams merge so that at some distance away from the emitters, the beams merge so as to effectively provide a single wedge-shaped beam extending some way on either side of the general ball flight path and with the wedge angle large enough to include the volume occupied by detection planes 19, 20 (see Figure 3) at ball trajectory height Alternatively, the beams axes may be tilted in the Y-Z plane away from the ball rest position 1 This alternative arrangement improves the spatial separation of a launched golf ball 1 * (see Fig 3) from the 'follow through clubhead 7* (see Fig 3) in the measurement zone A wedge shaped beam is still formed but the central axial plane of the wedge is tilted off vertical and away from the ball rest position

The RX array 15 comprises a top part which contains a plurality of narrow, elongate apertures 10, 11 12 and coacting with these apertures a plurality of sensor devices with associated circuitry arranged below the apertures and inside the RX array 15 so as to form a series of detection planes for measuring the direction and velocity of a launched golf ball 1 ^* The sensor devices are photo-electric sensors, such as light-detecting diodes

Three apertures 12 are co-linear and these are each used in conjunction with a respective pair of sensor devices to form two detection planes that are transverse to the Y direction (i e transverse to the general direction of ball flight) The two detection planes each comprise three smaller planes associated with the three co-linear apertures 12, and these smaller planes are nominally co-planar and merge to form the overall detection plane The purpose of using three smaller planes is to increase the detection zone to ensure that all ball trajectories pass through part of the overall detection plane This is particularly required for low trajectory shots where a single central aperture would not cover off-line shots The two main detection planes are shown (illustratively) by dotted lines 19 20 in Figure 3 The detection plane denoted by dotted line 19 is vertical whereas that denoted by dotted line 20 is at an angle to the vertical In alternative arrangements both planes can be at equal or different angles to the vertical and tilted in opposite directions in the Y- Z plane

A schematic view of an arrangement for analysing ball flight using such detection planes is shown in Figure 5 Two detection planes denoted by dotted lines 19 and 20 are normal to the page of the diagram As a launched golf ball 1 * passes through the planar light beam generated by the TX assembly 14, it reflects light back throughout a wide angle Some of this reflected light is incident on the RX array and passes through an aperture 12 to form a narrow slit of light Light sensors 50 51 are positioned below the aperture 12 and the fields of view that pass through the aperture from the two sensors form the detection planes centred along the dotted lines 19, 20 respectively After launch the golf ball 1 * flies above and over the RX array 15 and first passes through the detection plane denoted by dotted line 19 and then through the detection plane denoted by dotted line 20

Time variant signals corresponding to the passage of the ball through the respective detection planes are depicted in Figure 6 Waveform 52 exhibits a peak 53 corresponding to the instant in time when the ball 1 ^* is oositioned centrally in the detection plane denoted by dotted line 19 Similarly waveform 54 exhibits a peak at 55 when the ball is central in the detection plane denoted by dotted line 20 The waveform maxima are nearly flat and thus their exact time of occurrence are difficult to determine accurately by direct timing Preferably, the timing of the peaks is measured by capturing data from the rising and falling edges of the pulse waveform (on either side of a peak) and assuming that the pulse shape is symmetrical about its peak In theory, the maxima can be found to the necessary accuracy using only sparse data such as the timings of transitions above and below a fixed threshold on the rising and falling edges To allow for a wide variation in received signal level (signal dynamic range) it is useful to apply logarithmic compression of the pulse amplitude followed by level sampling using analog-to-digital converters or amplitude-to-pulse-width converters or other suitable techniques

In Figure 6 the pulse width durations pw1 and pw2 correspond to the passage of the ball 1 ^* through detection planes 19 and 20 respectively Note that pw2 is greater than pw1 because the ball takes longer to pass through detection plane 20 as this plane is more oblique (than detection plane 19) to the ball trajectory The pulse widths are proportional to the diameter of the ball 1 ^* and inversely proportional to the ball speed and to the sine of the angle subtended between the ball flight path and the detection plane The time separation (t2 - t1 ) between the pulse waveform peaks is also inversely proportional to ball speed and increases with the launch angle of the ball Thus the ball speed and launch angle can be calculated by solving three simultaneous equations equating ball speed, ball diameter and launch angle with the measured values of pw1 , pw2 and (t2 - 11 ) However, a simpler calculation is obtained if the time of initial launch of the ball is known The initial launch time t0' is (to within a very small and determinable error) equal to the time of impact and this can be accurately found from measurements of the clubhead position and velocity Alternatively, a direct measurement of the impact time using a microphone to detect the impact sound transient can be made Knowing t1 , t2 and tO, and assuming that the centre of the ball initially rests at the same horizontal level as the aperture 12, the elevation and speed of the ball can be found as follows -

tan(φ) = tan(α) (K /(1 + K)) ball speed = Ys/(cos(φ) (t1 - tO))

where φ is the ball launch elevation angle α is the angle of detection plane 20 relative to the horizontal

K is equal to (t2 - t1 )/(t1 - tO)

Ys is the distance between the ball resting spot and the vertical detection plane 19

Referring again to Figure 1 , it can be seen that the slit apertures 10 and 11 are arranged at oblique angles relative to the series of three collinear apertures 12 Coacting with each of the apertures 10 11 , there are provided one or more light sensors positioned vertically below the corresponding aperture so as to form one vertical detection plane for each aperture 10, 11 Thus, two nominally vertical detection planes are provided at oblique angles relative to the vertical X-Z plane In Figure 1 , dotted lines 19 21 and 22 denote the positions of vertical detection planes corresponding to apertures 12, 10 and 11 respectively It can be seen that this group of detection planes form a triangle with the planes also extending beyond the sides of the triangle By measuring (as described above) the time of arrival of the centre of a golf ball flying through two or more of the three detection planes 19 21 , 22, and knowing the speed of the ball, the azimuth direction of ball flight can be calculated in a similar manner to the calculation shown above for elevation angle

It will be appreciated that other arrangements of detection planes can be used to provide the measurement capability for fixing the ball flight direction in azimuth and elevation Each detection plane is coplanar with a slit aperture and at least one coacting light sensor Where two or more light sensors are used to form a detection plane, the signals from each sensor are combined to make one composite signal Two or more detection planes may also be formed using a single slit aperture (as exemplified in Figure 5)

Referring to Figure 3, the side of the TX/RX assembly 4 shows a series of vertical slit shaped apertures 23 on the front face 8 of the TX/RX assembly These apertures allow light reflected off the toe of a clubhead (during a pre- impact phase) to be incident on corresponding light sensors placed at appropriate positions at some distance behind the front face 8 The primary light source that provides the incident light on the clubhead comprises high intensity IR emitters 25 and these may be mounted on the front face 8 so that only back reflected light from the emitters is incident on light sensors behind the front face The emitted IR light may be continuous or pulsed

Preferably, two modes of light emission are provided In a standby mode, very short duration pulses are emitted from at least one emitter and operating in low duty cycle so as to conserve standby power A wide angle photodiode 26 with appropriate fast response detection circuitry monitors the level of any light reflected back from an object in the field of view If this level is above a threshold indicating the presence of reflection from a clubhead or equally reflective object the system switches into data capture mode with longer pulse duration and/or higher duty cycle The data capture mode is maintained for a duration greater than the maximum dwell time of a clubhead in the measurement zone taking account of the slowest expected swing speeds Alternatively, the data capture mode may be stopped by an interrupt that is generated from an acoustic sensor or other means when the clubhead impacts the ball

The receiver part of the TX/RX assembly 4 operates in a similar manner to the RX array 15 described above, except that the ball is replaced by a circular reflector zone or highlight 27 attached to the toe 9 of a clubhead 7 and this moves in a direction approximately parallel to the row of apertures 23 The highlight 27 passes through a series of detection planes formed by the apertures 23 and associated light sensors, and this enables the clubhead speed, swingpath angle and off-centeredness (impact point) to be determined Two additional slit apertures 60, 61 are orientated at an angle to the vertical and in conjunction with light sensors placed some distance behind, provide two detection planes (denoted by dotted lines 62 63) that are normal to the Y-Z plane but tilted at a known angle (or angles) to the vertical The detection planes 62 63 enable measurements of clubhead elevation path (attack angle) and height at impact

The schematic diagrams of Figures 1 , 2 and 3 illustrate the essential features of a typical embodiment of the invention and for convenience have not been drawn to scale Scale drawings illustrating mechanical aspects of a preferred embodiment are shown in Figures 7 and 8 This shows the relationship between a golf ball 1 and apparatus comprising a TX/RX assembly 4 and a cover 70 Figure 7 also shows the nominal positions of four vertical detection planes that are necessary to implement measurements of clubhead speed, swingpath and impact offset These detection planes are denoted by dotted lines 64, 65, 66 67

It is advantageous to design the apparatus to be unobtrusive and also well clear of the ball resting position so that the chance of accidental collision between a clubhead and the apparatus is negligibly small Thus the overall height 'h' is preferred to be not greater than the height of the centre of the golf ball 1 on its tee 2 (i e 30mm or less) Also the separation 'd' between the tee spot and the top edge of the apparatus is typically 24cm or greater, giving a generous margin of clearance so that the apparatus is well out of range of wayward clubhead swingpaths The size of the slit apertures used will depend on the required geometry of the system but they will typically have a length in the range 5 - 30 mm and a width of 1 mm or less and preferably 0 25 mm or less

The apertures 23 are preferably formed at or near the same distance d from the tee spot, and the associated light sensors are typically a further 0 5d beyond the apertures so that the overall distance from tee spot to light sensing devices is typically 36cm However other distance ratios can be adopted In this context, note that for the ball trajectory detection system (TX 14, RX 15) the distance between the sensors and apertures would be typically 25mm with the distance between the ball and apertures in a range from a few centimetres to 50cm or more This greater ratio of distances (compared with the clubhead measuring system TX/RX 4) is allowed because the required accuracy of ball position measurement is proportionally less

An accidental miss-hit of a golf shot sometimes results in a ball flying very low and at almost 90° to the intended direction This results in the ball striking the front face 71 of the apparatus However the imparted ball speed is a small fraction of the clubhead speed, since it is the outcome of a very oblique deflection off the toe of a clubhead Thus the energy imparted to the ball is very low relative to normal golf shots and it is thus possible to design the cover 70 to withstand this degree of impact In this respect it is advantageous to provide the cover with a sloping front face 71 This results in an oblique impact from a low trajectory ball and further reduces the impact shock on the cover The slope angle of the front cover is preferably less than 45° relative to the horizontal, as this ensures that a low trajectory ball does not bounce back towards a player after striking the cover

The front cover 71 must be sufficiently transparent to IR light to allow proper operation of the TX/RX assembly 4 In one preferred embodiment, the whole cover assembly 70 is fabricated from a high impact and scratch resistant plastic containing a dye that forms an IR transTnissive filter while being virtually opaque to visible light Optionally, the cover can be provided with a cladding that acts both as an impact cushion and a cosmetic covering In this case the cladding must be selectively removed where necessary to permit correct reception and transmission of IR light to and from the TX/RX assembly 4

In a similar manner the TX array 14 and RX array 15 (Figure 1 ) are protected from damage by ball impact using a form of impact deflector suitably positioned to cushion and/or deflect low trajectory balls that could result from 'topped' shots As the height (i e the thickness) of the tee-off mat 3 is typically 30mm or greater the overall height of the TX array is preferably made equal or less than this height so that a 'topped' golf ball flies clear of the TX array The arrays 14, 15 are preferably constructed as an integral unit and mechanically linked to the TX/RX assembly 4 so as to maintain correct alignment

It will be appreciated that TX/RX assemblies 4 and 14, 15 may be positioned at the edges of a tee-off mat and that with the arrangement described, no emitters or sensors are required in the mat Figures 4A and 4B show toe-side views of an iron' type clubhead 28 and a 'wood' type clubhead 29 modified for use with the invention Diffusely reflecting highlights 30 31 are positioned on or near the extreme toe parts of the clubheads Matt black surface areas 32, 33 surround these reflecting highlights and cover the parts of the toe regions that could direct strong reflections from the IR emitters 25 back towards the TX/RX assembly 4 The matt black surface areas 32, 33 are designed to have as low a reflectivity to incident IR light as is practical, and any surface form that achieves this aim may be used The reflecting highlights 30 31 are typically brilliant white surfaces or they may be highly reflecting polished surfaces with an overlay of translucent light diffusing material The reflecting highlights should ideally emulate the characteristics of a perfectly diffusing reflector with a lambertian pattern of reflected light intensity

The clubhead 29 is typical of the clubhead used in Figure 1 The highlight 31 is in the form of a circular area with two lateral triangular segments removed It will be appreciated that the quantity of light reflected from this form of highlight increases in approximately a linear manner as the centre of the highlight 31 passes into a detection plane, and then decreases in a similar manner as it passes beyond the plane so as to provide a signal with more clearly defined maxima compared to that shown in Figure 6 Also, as the clubhead rotates about the X axis (for small angular rotations, typical of clubhead behaviour) the same general shape and peak amplitude of response is maintained Thus, the purpose of removing the triangular segments from the circle is to shape the obtained signal response and increase the detectability of the centre of the highlight

It should be noted that for the greater part of a clubhead surface area, namely those areas that face away from the TX/RX assembly (during a 'normal' or 'acceptable' golf swing), the surface finish is advantageously highly polished or glossy as is normally the case in traditional golf clubs On such areas, incident light from the IR emitters 25 is efficiently reflected but always directed away from the TX/RX assembly In particular all the top surface of a clubhead and also the hosel ferrule and shaft of a club come into this category This is exemplified in Figures 1 and 2 where a light ray 34 is incident on the top surface of the clubhead 7 and a sharply (as distinct from diffusely) reflected light ray 35 is directed away from the TX/RX assembly It is thus evident that the modification to a standard club comprising a reflecting highlight 30 or 31 and non-reflecting surrounding area 32 or 33 can be hidden from the view of a golfer as he or she plays a shot

In its simplest form, the modification to a standard clubhead comprising the reflecting and non-reflecting portions can be provided as a self adhesive printed label, but other forms of modification can be provided For example, lightweight rubber or plastic moulded attachments can be provided, and this also allows modification of the surface profile to optimise the light source characteristic If a second highlight on a clubhead is provided, it is preferable to position this remote from the toe highlight, for example on the back of a clubhead and near the heel or on the hosel This allows measurement of clubface angle and rotation providing the positions of the highlight centres are accurately known in relation to the clubface

Referring now to Figures 9 and 10, the outputs from discrete sensors 100, 101 are amplified and give rise to signals V3 and V4 respectively The two sensors are positioned in vertical relationship and receive light through an aperture stop 102 that provides a vertical slit aperture The resulting combined angle of view contains two detection planes that are coplanar, vertical and overlap in the region 103 (shown shaded) It will also be noted that the detection plane defined by sensor 100 terminates just above the surface of the tee-off mat 3. A clubhead 28 is provided with a vertical triangular shaped highlight 30 (as illustrated in Figure 4B) The highlight 30 is symmetric about the vertical when the clubhead 28 is in properly grounded position As the clubhead passes through the overlapping detection planes part of the highlight 30 extends beyond at least one of the two planes Comparison of the signal waveforms (V3, V4) allows an estimate of the height of the clubhead as it passes through the detection planes Additionally, the relative slope of the leading and trailing edges of the signal waveforms allows an estimate of the clubhead dynamic loft (i e rotation about the X axis)

In a preferred arrangement, two sensors 100, 101 are used with a single slit aperture as shown in Figure 9 and the clubhead is provided with a first highlight 30 on the toe as described above and a second highlight 30A on the hosel If the spacing between the sensors 100 101 corresponds to the length of the slit aperture eg both being around 15 mm the overlap region 103 will have parallel sides and if the width of this region is less than the vertical dimension of the highlight 30 this ensures that the signals received by the two sensors 100, 101 differ so information on the vertical position of the clubhead can be deduced therefrom As indicated above, measurement of the waveform produced by the highlight 30 allows the dynamic loft of the clubhead to be estimated The data received from the two highlights 30, 30A also enables the dynamic lie of the clubhead le its rotation about the Y axis to be estimated

The arrangement of Figure 9 allows the overall height of the combined detection plane at the clubhead to be increased by having sensor 101 placed below the level of the tee-off surface Thus, the vertical range required in the detection plane can be provided using a reduced length aperture and thus a relatively low profile housing

Referring now to Figure 10, typical waveforms for V3 and V4 show how height and tilt of the clubhead 28 can be measured The rate of rise of the leading edges 104 105 of the waveforms are steeper than the respective trailing edges 106 107 and this indicates that the clubhead was de-lofted as it passed through the detection planes Also, the waveform shapes show that only a lower part of the highlight 30 passed through the field of view of sensor 100, and that most of the highlight, including the upper portion passed through the field of view of sensor 101 Detailed analysis of the waveforms allows precise measurement of the height and dynamic loft of the clubhead through the detection planes

Referring now to Figures 11 and 12, a further embodiment of the invention is shown where a three-terminal position sensitive detector (PSD) device 136 coacting with a pulse modulated LED highlight 141 is used in place of discrete sensors and diffusely reflecting highlights In this arrangement battery power and control circuitry for the LED 141 must be provided on the clubhead The PSD is connected to driver and signal processing circuitry 137 A voltage bias is applied to terminal 140 with respect to terminals 138 and 139 ana the currents h and flowing out of terminals 138 and 139 respectively are measured and recorded These currents are proportional to the total incident light on the PSD. plus a very small component of 'dark current Radiated light from the LED highlight 141 passes through a slit aperture 142 and forms a light spot 143 on the PSD The position of this light spot along the active length L of the PSD varies as a function of θ, where θ is the angle subtended between a centreline 144 and the line of sight between the highlight 141 and the aperture 142 The relationship between the currents flowing out of terminals 138 and 139 and the angle θ can be expressed as follows - tan(θ) = (U2 D) ((h - h)/(lι + ))

where D is the separation between the aperture 142 and the photosensitive surface of the PSD

The above equation assumes that dark current and photocurrent from other ambient light sources are negligible and that the PSD is ideal and centrally aligned with the aperture In Figure 12, two highlights 141 a and 141 b represent two possible vertical positions of the single highlight that is shown in plan view in Figure 11 The position of the vertical slit aperture is shown in dotted outline 145 Light from highlights 141 a and 141 b passing through this aperture forms two vertical light slits 143a and 143b respectively These light slits are in-line and partially overlap, and it can be seen that light from both positions 141 a and 141 b of the highlight form a light spot on the same part of the elongate surface of the PSD 136 Thus, although the magnitudes of the current signals may change, the ratio of their sum and differences as given above does not vary with vertical displacement Thus, the PSD 136 and slit aperture 145 effectively provide a set of vertical detection planes, each corresponding to a successive pulse emission of the LED highlight 141 and the angular directions of these detection planes about the Z axis can be determined by measurement of the PSD currents

In a further embodiment, rather than using wide angle light emitters as described above and sensors with a field of view defining a detection plane, the emitters may instead be arranged to emit light only in a given plane and wide angle sensors used to detect when light is reflected from this plane Thus, in this arrangement, the light emitters define the detection plane e g by use of a slit aperture adjacent a light source, rather than the light sensors If more than one detection plane is used in this arrangement, it may be necessary to time complex the emitters to avoid signals from the different detection planes interfering with each other

The invention has been described above with particular reference to the motion of a golf clubhead and/or the motion of a golf ball during execution of a golf shot but it will be appreciated that apparatus operating on the principles described above may also be used in measuring parameter relating to the trajectory and/or motion of moving articles in other applications

Claims

CLAIMSApparatus for measuring parameters relating to the trajectory and/or motion of a moving article the apparatus comprising one or more light sources for providing light emitted from or reflected by the moving article and one or more light sensing means each arranged to provide a signal when the respective sensing means is illuminated by said light, wherein at least one of the light sensing means is arranged to detect when the moving article intercepts a given detection plane wherever the article intercepts the detection plane the arrangement being such that the position and orientation of the detection plane relative to a reference point is known or can be deduced from the signal provided by the said at least one sensing meansApparatus as claimed in Claim 1 in which the light sensing means comprises one or more discrete light sensors and a slit shaped aperture and/or a cylindrical lens associated therewithApparatus as claimed in Claim 2 in which the light sensor comprises a photo-electric deviceApparatus as claimed in Claim 1 in which the light sensor comprises a linear light sensor and a circular aperture and/or spherical lens associated therewithApparatus as claimed in Claim 1 in which the light sensing means comprises a linear light sensor and a slit aperture and/or cylindrical lens associated therewithApparatus as claimed in Claim 4 or 5 in which the linear light sensor comprises a linear array of charged couple devices (CCDs) Apparatus as claimed in Claim 4 or 5 in which the linear light sensor comprises an one-dimensional position sensitive detectorApparatus as claimed in any preceding claim in which the one or more light sources comprise one or more static light emitters for illuminating a reflective portion of the moving articleApparatus as claimed in any of Claims 1 - 7 in which the one or more light sources comprise one or more light emitters carried by the moving articleApparatus as claimed in any preceding claim in which the one or more light sources are arranged to provide pulsed lightApparatus as claimed in any preceding claim in which the detection plane is defined by the sensing means having a relatively wide angle of view in one plane of at least 5 degrees and a relatively narrow angle of view in a perpendicular plane of 1 degree or less and preferably 0 25 degrees or lessApparatus as claimed in any preceding claim in which the sensing means is arranged to define at least two detection planesApparatus as claimed in claim 12 in which the sensing means comprises two light sensors and a single slit aperture and/or a cylindrical lens associated therewithApparatus as claimed in claim 13 arranged such that the two detection planes are co-planar and partially overlap Apparatus as claimed in any preceding claim comprising data processing means for processing signals provided by the said at least one light sensing meansApparatus as claimed in Claim 15 in which the data processing means is arranged to analyse the form of each signal provided by the light sensing means to determine accurately the timing of the signalApparatus as claimed in Claim 15 or 16 in which the data processing means is arranged to analyse the signals from the light sensing means to determine parameters relating to the trajectory and/or motion of the moving articleApparatus as claimed in any preceding claim having article sensing means for sensing when the moving article is present and activating the light sources and/or light sensing means accordinglyApparatus as claimed in any preceding claim in combination with one or more articles the movement of which is to be sensed, the or each of the articles being provided with a reflective portions and/or light emitting meansApparatus as claimed in Claim 19 in which the article is provided with reflective means comprising a diffusely reflective region surrounded by a relatively non-reflective regionApparatus as claimed in Claim 20 in which the diffusely reflective region is shaped so as to provide a well-defined maxima in the signal produced by the sensing means when the reflective region passes through a detection plane Apparatus as claimed in claim 20 in which the diffusely reflective region is shaped so as to enable information on its orientation relative to the detection plane as it passes therethrough to be determined from the signal produced therebyApparatus as claimed in Claim 19 in which the article is provided with light emitting means preferably a light emitting diode together with a power source thereforApparatus as claimed in any preceding claim for use in measuring parameters relating to the trajectory and/or motion of a golf clubhead and/or a golf ball during the execution of a golf shotApparatus as claimed in Claim 24 in which the light sensing means are provided in a housing for positioning on the ground at a distance from the tee-off position of the golf ballApparatus as claimed in Claim 25 arranged to measure the said parameters when positioned on the ground at a distance of at least 24 cm from the tee-off positionApparatus as claimed in Claim 25 or 26 in which the housing has a maxima height of 50 mm or lessApparatus as claimed in Claim 25 comprising two sets of light sensing means provided in respective housings for positioning on the ground at different locations relative to the tee-off positionApparatus for measuring parameters relating to the position and/or trajectory of a moving article substantially as hereinbefore described with reference to the accompanying drawings A golf club for use with apparatus as claimed in any preceding claim, the golf club being provided with at least one diffusely reflective region surrounded by a relatively non-reflective regionA golf club as claimed in Claim 30 in which the diffusely reflective region is shaped so when passing through a detection plane, the intensity of light reflected therefrom goes through a well-defined maximaA golf club as claimed in Claim 30 or 31 in which the diffusely reflective region and/or the relatively non-reflective region are provided thereon by means of a self-adhesive stickerA golf club for use with apparatus as claimed in any of Claims 1 - 29, the golf club being provided with at least one light emitting means preferably a light emitting diode, together with a power source thereforA golf club substantially as hereinbefore described with reference to the accompanying drawingsApparatus for measuring the pre-impact and post-impact position and/or motion of a golf clubhead and/or of a golf ball during execution of a golf shot, the apparatus comprising light sensing means having a field of view which comprises at least one detection plane and arranged to sense light reflected from or emitted by the clubhead and/or the ball as it passes through said detection plane AMENDED CLAIMS[received by the International Bureau on 25 March 1998(25.03.98) ; original claim 1 amended ; remaining claims unchanged ( 1 page) ]

1. Apparatus for measuring parameters relating to the trajectory and/or motion of a moving article, the apparatus comprising one or more light sources for providing light emitted from or reflected by the moving article and one or more light sensing means, each light sensing means being arranged to provide a signal when it is illuminated by said light, wherein the light sensing means or the light source define one or more detection planes and at least one of the light sensing means is arranged to detect when the moving article intercepts a given detection plane wherever the article intercepts the detection plane and is arranged to sense variations in the said signal as the article passes through the detection plane, the arrangement being such that the position and orientation of the detection plane relative to a reference point is known or can be deduced from the signal provided by the said at least one sensing means.

2. Apparatus as claimed in Claim 1 in which the light sensing means comprises one or more discrete light sensors and a slit shaped aperture and/or a cylindrical lens associated therewith.

3. Apparatus as claimed in Claim 2 in which the light sensor comprises a photo-electric device.

4. Apparatus as claimed in Claim 1 in which the light sensor comprises a linear light sensor and a circular aperture and/or spherical lens associated therewith.

5. Apparatus as claimed in Claim 1 in which the light sensing means comprises a linear light sensor and a slit aperture and/or cylindrical lens associated therewith. STATEMENT UNDER ARTICLE 19

Claim 1 has been amended to clarify the fact that the apparatus uses detection planes and to indicate the sensing means is arranged to sense variations in the signal received as the article being sensed passes through a detection plane. The use of detection planes greatly simplifies the apparatus and allows more information to be obtained. The majority of the cited prior art does not disclose the use of detection planes. US3759528 discloses the use of sensor heads which are arranged to respond to light reflected from a restricted area, e.g. three vertical planes. Sensing variations in the signal received as the article passes through a detection plane is not, however, disclosed in the prior art. Sensing such variations enables more information and more accurate information to be obtained as described in the present application.