GB2419298A

GB2419298A - Methods and systems responsive to golf-ball landing impacts

Info

Publication number: GB2419298A
Application number: GB0521674A
Authority: GB
Inventors: Norman Matheson Lindsay
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-10-22
Filing date: 2005-10-24
Publication date: 2006-04-26
Also published as: GB0521674D0; WO2006043091A3; WO2006043091A2

Abstract

Response to golf-ball landing-impacts within a landing area 4 is provided by mutually-spaced piezoelectric-cable sensors 1,2;11-14;21,22 to provide voltage signals that are analysed to determine impact-location in the area 4 in dependence upon their relative amplitudes, the peak-amplitude difference between the signals or upon the difference between their peak-amplitude averages, or their root-mean-squares. The sensors are arranged in concentric circles 1,2 or in straight, parallel lines 11-14; there may be two straight sets 21,22 orthogonal to one another. The analysis may involve determining whether the sum of two of the signals exceeds a threshold and whether their difference is positive or negative. Where there are more than two sensors 11-14;21,22 the signals of largest amplitude are selected for determining impact-location.

Description

Methods and Systems Responsive to Golf-Ball Landing Impacts This invention

relates to methods and systems responsive to golf-ball landing impacts.

The invention is applicable especially, though not exclusively, to methods and systems for use in golf-ball to driving ranges for responding to golf-ball landing impacts at target areas.

It is known from WO-A-92/01494 to use geophones distributed around the area of a golf target to sense the impact of a ball as it lands. Electric signals are generated by the geophones in response to vibrations from the impact, and the relative timings of the peaks of the respective signals are analysed to determine the position of ball-impact. However, geophones are expensive and several hundred are required in a typical instrumented golf-driving range. Moreover, the requirement to measure timing differences in the phase of the generated signals demands a high signalsampling frequency and sophisticated signal processing.

It is an object of the present invention to provide a method and system responsive to golf-ball landing impact that are more economic and less demanding in regard to signal processing than the known method and system.

According to one aspect of the present invention there is provided a method for responding to golf-ball landing-impacts within a landing area, wherein a plurality of elongate pressure-sensitive sensors are spaced from one another within the landing area, each sensor is responsive along its length to the incidence thereon of a pressure-wave created by impact of a golf ball landing within the area, to provide a signal dependent on the incident wave, and wherein signals provided by the individual sensors in response to a golf-ball impact are analysed to derive therefrom representation of the position of that impact relative to the sensors.

According to another aspect of the present invention a system for responding to golf-ball landing-impacts within a landing area, comprises a plurality of elongate pressure-sensitive sensors that are spaced from one another within the landing area, each sensor being responsive along its length to the incidence thereon of a pressure-wave created by impact of a golf ball landing within the area, to provide a signal dependent on the incident wave, and means for analysing the signals provided by the individual sensors in response to a golf-ball impact to derive therefrom representation of the IS position of that impact relative to the sensors.

The analysis of the signals provided by the sensors may be related to the difference of timing or phase between the signals provided by the sensors, but it is preferred to relate it to the amplitudes of the signals. In the latter respect, the analysis of the signals may determine the position of impact as dependent on the relative amplitudes of two signals provided as aforesaid by the sensors in response to that impact. More particularly, the position of impact may be determined as dependent on peak-amplitude difference between the two signals, or on the difference between an average of the peak amplitudes of one of the two signals and a corresponding average of the other signal, or on the difference between root-mean-squares of the amplitudes of the two signals.

The sensors may be located above the surface of the landing area to respond to pressure-waves transmitted through the air, or may be located on the surface itself, but are preferably located below the surface to respond to pressure- waves transmitted through the ground, artificial turf or other medium such as water. They may be elongate 1 piezoelectric cables, and in this respect may be of coaxial construction. Each sensor is preferably of a length L which is at least equal to the spacing S between it and the next sensor, and may be buried at substantially uniform depth.

The spacing S is preferably substantially constant between adjacent sensors and in this respect the sensors may extend substantially circumferentially of respective concentric circles within the landing area. For example, two mutually spaced sensors in the form of piezoelectric cables may encircle a target in a driving-range or golf course at an average distance R from the centre of a target landing area such that an inner sensor is laid along a circle having a radius of(R S/2) and an outer sensor is laid along a circle of radius (R + S/2) . The purpose of this sensor arrangement is to determine whether a ball lands inside or outside the circle of radius R. This can be readily determined from the sum and difference of the amplitudes of the signals provided by the two sensors. When a golf ball lands anywhere on the circle R. the sum of the amplitudes is large and the difference is nominally zero, whereas when it lands inside the circle the difference between the amplitudes is comparable with their sum and of a certain sense, positive or negative. However, when the ball lands outside the circle the difference between the amplitudes is again comparable with the sum but is of the reverse sense.

The radius R may be typically 5 metre and the spacing S typically 1 metre or less, giving the ratio L/S in this case a value of thirty or more. The radius R may vary slightly to follow a non-circular boundary round the target, but the spacing S should desirably be substantially constant so as to maintain equal measurement-sensitivity round the boundary.

As an alternative, the sensors may extend in substantially straight lines parallel to one another, and furthermore, there may be two sets of sensors with the sensors of each set extending orthogonally to the sensors of the other set within the landing area. For example, in a sensor array comprising two orthogonal sets of sensors the ratio L/S may be typically greater than 5, and the spacing S between all adjacent, s parallel sensors substantially constant throughout at less than 5 metre or D/50, where D is the distance of the target from the driving bay. Thus, for a chipping practice target at 25 metre range, it is preferable for the spacing S to be centimetres or less since balls landing on such a close range target have low landing impact energy and close spacing between sensors ensures high sensitivity and adequate signal- to-noise ratio. By contrast, for a distant target at 200 metre, the value of S may be 4 metre or less since balls landing at around 200 metre will have high landing energy IS that can be reliably detected at up to 4 metre; moreover, the absolute measurement precision required for distant targets is less than for close-range targets.

If the driving range is provided with an artificial surface, the sensors can be laid directly below this surface rather than buried in the soil. Preferably, such artificial surface has special attributes that enhances the performance of the measurement system. For example, it is desirable that most of the energy of a descending ball is absorbed on the first landing impact so that the second impact from a bounce has little energy and can be reliably rejected by signal discrimination means. In this respect it is desirable that the rebound coefficient of an artificial surface is not more than 0.1 or preferably not more than 0.03; the rebound coefficient is the ratio of the height of bounce of a dropped golf ball to the height from which it was dropped.

The relationship between impact position and signal amplitude is nonlinear and can vary with temperature and the water content of the soil. It is thus desirable to have a means of calibrating the amplitude versus impact-position characteristic. For many applications, an approximate s expression is sufficient since the required precision can be obtained by closely spacing the sensors. Thus, with a spacing of D/50 or less, the landing position can be reliably determined to within +1% of range (which is equivalent to S +0.5S) using just one test to determine if an amplitude ratio is above or below a fixed value. Where greater precision is required, data from a large sample of impacts can be used to determine the relationship between landing position and signal amplitude ratios Methods and systems in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings in which: IS Figures 1 and 2 are illustrative as a first example of a system according to the invention, of a target area of a golf-driving range, Figure 1 providing a schematic plan view below ground level of the target area, and Figure 2 a schematic sectional side elevation of the target area; Figure 3 is a circuit diagram of an electronic amplifier and signal detection circuit used in the system of Figures 1 and 2; Figures 4 and 5 show electric signal waveforms generated in the system of Figures 1 and 2 in response to the impact of a golf ball landing in the target area; Figure 6 illustrates graphically aspects of analysis of electric signals generated in the system of Figures 1 and 2; Figure 7 is a schematic representation of a second example of system according to the invention; Figure 8 is a graph of the signal response of the system of Figure 7; and Figure 9 is a schematic plan view of a third system according to the invention.

Referring to Figures 1 and 2, two elongate piezoelectric cable sensors 1 and 2 are laid flat round a target-flagpole 3. The sensors 1 and 2 are each buried at a depth of between to 50 centimetres below the landing surface 4 of the target area, but where the landing surface 4 is a layer of synthetic turf or the like, they may be laid directly underneath that layer. Each sensor 1 and 2 is connected at one end to a signal-conditioning and data-acquisition unit 5 via a respective cable 6 that is inert in the sense that it is unresponsive to vibration.

IS Sensor 1 extends circumferentially of a circle of radius (R S/2) centred on the flagpole 3, whereas sensor 2 extends circumferentially of a concentric circle of radius (R + S/2).

The radius R and the spacing S between the two sensors 1 and 2 in the case of a medium-range target, may be 5 metre and 1 metre respectively, giving a ratio L/S larger than 30. The phase of a ground- borne pressure wave front emanating from impact at the centre of the circular configuration of each sensor 1 and 2 is identical at all locations along the sensor-length so there is no loss of signal due to phase non coherence within it. Thus, the circular configuration sensors 1 and 2 maintains good sensitivity to impacts near the flagpole 3 as well as to impacts closer to the sensors 1 and 2 themselves.

Protection of the system against lightning strike, is provided where, as in the present example, the target- flagpole 3 also acts as a lightning conductor. In this respect, the flagpole 3 is made from, or incorporates, a conductive material and its lower end 7 is driven deep into the ground to provide a ground connection of low impedance that is preferably less than 10 ohms. It is generally accepted that a lightning conductor of this form protects any object within a cone having a half-angle of 45 degrees as indicated in Figure 2 by the dashed lines 8. Thus, if the flagpole 3 is H metre high, the unit 5 and any other associated, sensitive electronic equipment should preferably S be not more than H metre distant from the flagpole 3 when at ground level and more preferably within H metre and below ground level as shown. Any communications link from the unit or other electronic equipment in the target area for conveying data to a distant part of the overall driving-range system may be by means of an optical-fibre link, which is inherently immune to lightning. Alternatively, the communications link may be via a wireless transmitter/receiver with lightning protection on its aerial.

The target surface 4 may be slightly sloping as shown in Figure 2 so that balls landing on or near the target roll away from the sensors l and 2 after impact and into a collection sump (not shown) via sloping trenches (not shown).

It is preferable that the surface 4 absorbs most of the energy of an impacting ball but also provides low rolling friction, and where synthetic turf is used for the surface 4 its characteristics may be selected to have a low golf-ball rebound coefficient (measured by the ratio of the height of bounce of a dropped golf ball to the height from which it was dropped), for example, not more than O.l, or more preferably not more than 0.03. This ensures that the sound pressure intensity of a ball landing from a bounce is below -20 dB or -30 dB respectively, relative to the landing impact intensity. It is also desirable to provide low rolling friction so that golf balls roll off the target area readily.

The unit 5 incorporates a circuit of the form shown in Figure 3 for interfacing with each sensor l and 2 via its respective cable 6. In this regard each piezoelectric-cable sensor l and 2 has an equivalent circuit as represented in Figure 3 by a voltage source Vl in series with a capacitor C1.

Variations in the voltage from source Vl are proportional to the instantaneous pressure variations averaged over the length of the piezoelectric cable and gives rise to charge variations through capacitor C1. A surge arrestor circuit comprising impedances Z1 and Z2 (which may be resistive or inductive), diodes D1 and D2 and a capacitor C2, provides differential and common-mode protection to an input amplifier A1 and subsequent circuitry. Surge protection is desirable to provide some degree of immunity against nearby lightning strikes.

The input amplifier A1 and a feedback capacitor C3 convert the chargevariation signal from the piezoelectric sensor 1 or 2 to a voltage signal on the output of amplifier A1, and a feedback resistor R1 prevents large drift voltages due to amplifier-input offset, building up on the output of the amplifier A1. The RC time constant of the shunt-connected resistor R1 and capacitor C3, however, is very large compared with the period of the signal waveform resulting from golf- ball impact, so the gain of the amplifier A1 is not significantly reduced at the frequencies of interest. An additional filter stage may be provided to reject out-of-band noise signals.

Amplifier A2 acting in conjunction with feedback diodes D3 and D4 and resistors R2 and R3, provides voltage gain and precision half-wave rectification of the voltage output at A1. The positive peak voltages are stored on a capacitor C4, and this stored voltage decays with a time constant that is mainly determined by the resistor R4 and capacitor C4. The output voltage VO across the capacitor C4 is sampled as required by a data acquisition circuit (not shown) of the unit 5.

In an improved implementation of the circuit of Figure 3, the half-wave rectification stage is replaced by a stage providing full-wave rectification or, more preferably, true RMS to DC conversion. Other methods of signal processing may be applied, including digitising the waveform and applying adaptive filtering techniques. Furthermore, provision for periodically testing the gain and frequency-response of the interface channel and detecting open- and closed-circuit S faults may be made by connecting a silicon diode (not shown) across the remote end of each piezoelectric-cable sensor 1 and 2 and inputting a modulated test current to the respective cable 6.

The voltage waveforms of Figures 4 and 5 are illustrative of the amplified (but not rectified or otherwise converted) responses of the two sensors 1 and 2 to an impact representative of a golf ball landing with about 20 metre per second descent velocity at a point between them (each IS waveform is plotted against a time-scale in milliseconds, for which zero signifies the instant at which the waveform initially exceeds a threshold of 0.1 volt). The sensors 1 and 2 have a spacing S of 5 metre and the landing point is assumed in this case to be 2 metre from the sensor 1 and 3 metre from sensor 2, resulting in an amplified response from the sensor 1 as illustrated in Figure 4, and from the sensor 2 as illustrated in Figure 5. The signal of Figure 5 is about -8dB relative to the signal in Figure 4 and the two waveforms although having the same fundamental frequency of about 55 Hz, have significantly different pulse-envelope shapes.

The measurements of Figures 4 and 5 relate to ball-impact on a clay-soil surface where the velocity of ground-borne pressure waves is of the order of 1000 metre per second. If in these same circumstances the relative times of arrival of pressure-wave pulses are used to determine differences in ball-landing positions, then it is necessary to discriminate differences of 1 millisecond or less in the relative times of arrival in order to be able to resolve landing positions to within 1 metre. However, it is sometimes required to resolve landing positions to within 30 centimetre or less, so it follows from the signal waveforms of Figures 4 and 5 that detecting differences in times of arrival of l millisecond or less requires advanced signal-processing techniques such as signal-correlation processing and also requires sampling frequencies greater than l kHz.

In the present method and system, relative amplitudes of the detected sensor signals are used in preference to relative phase or timing differences, though use of the latter differences are not excluded as a possibility. As illustrated by comparison of Figures 4 and 5, ball-impact position has a large influence on signal amplitude, so measuring and comparing amplitude variations provides a very reliable means of measuring the distance of ball-impact relative to the sensors l and 2. The relative amplitude difference may be measured as peak-amplitude difference, but more preferably as the difference between the average of peaks in the individual waveforms or the root-mean- square (RMS) values of the waveforms averaged over (typically) 20 to lOO milliseconds.

The sum of, and the difference between, the signal amplitudes from the sensors l and 2 are used to determine whether a ball lands to one side or the other of the line or curve mid-way between them. Figure 6 shows how the amplitudes of signals that are obtained from combinations of the amplified signals derived from sensors l and 2, vary according to position The solid trace of Figure 6 is proportional to (Vl - V2) and the dashed trace is proportional to (Vie + V2), where Vie and V2 are RMS or average peak voltage signals derived from sensors l and 2 respectively. The values of these difference and sum terms are dependent on the energy of landing-impact as well as the position of the impact relative to the sensors l and 2. For this reason, these terms do not provide a reliable means of measuring general variations in impact position, but they can be used for determining accurately whether a landing impact is inside or outside the circle of radius R. Provided the sum(V + V2) is above a threshold, then a positive value of the difference(V - V2) indicates that the landing point is inside the circle and vice versa.

In addition to measuring where balls land, measurements of when they land may also be provided so that, for example, it can be used in conjunction with measurement of when the ball was hit to calculate duration of flight. It is not usually required to determine landing times to less than +50 milliseconds or even +250 milliseconds, and in this context the landingtime of a ball is derived in the present system by averaging the RMS or peak amplitude of the sensor-signal over several tens of milliseconds. The data sampling frequency used can advantageously be as low as 20 Hz or less.

By making the data sampling frequency equal to the local powerdistribution frequency or one-half or one-third of it, interference from nearby power distribution sources is rejected. Thus, it is preferable to use sampling frequencies of 50 Hz, 25 Hz or 16.67 Hz in Europe or 60 Hz, 30 Hz or 20 Hz in North America.

More than the two mutually-spaced concentric sensors 1 and 2 may be used, and their radii and the spacings S between the individual pairs of adjacent sensors may be larger or smaller than for the example described above. For example, it may be required to detect if a ball-impact is within distances such as 4.6 metre (5 yard) and 9.1 metre (10 yard) of the flagpole 3. In this case, the inner sensor pair may have radii R of 4.2 metre and 5.0 metre with spacing S of 0.8 metre and the outer sensor pair may have radii R of 8.5 metre and 9.7 metre with spacing S of 1.2 metre. A non-circular configuration may be adopted but it is again preferable (but not a limitation) for the spacing S between adjacent sensors to be substantially constant. In a further embodiment, the two spaced apart sensors may be straight and parallel to one another to detect whether a ball lands on one side or the other of a straight boundary. / ]2

The ratio of the two largest-amplitude signals from three or more adjacent sensors can be selected for use to determine the position, perpendicular to the sensors, of any arbitrary S landing spot in a defined area bounded by them. In this regard, Figure 7 is a schematic end view of four sensors 11, 12, 13 and 14 buried a few centimetres below a landing surface 15. This arrangement provides a means of measuring the left-to-right landing position (as viewed in Figure 7) of lo balls landing anywhere in a zone from mid-way between sensors 11 and 12 to mid-way between sensors 13 and 14. In Figure 7, the limits of this zone are indicated by the dashed lines 16 and 17. Balls that land to the left of dashed line 16 or to the right of dashed line 17 can be detected, but it is only possible to make an approximate estimate of their landing positions. However, the left-to-right impact position of a ball landing between dashed lines 16 and 17 can be determined very accurately from the ratio of the two largest-amplitude signals produced in the sensors 11 to 14 by the ball-impact.

In this respect, it is useful to define a ratio factor F by: VHI + X (VHI + VLO) VLo+5X(VHI+VLO) where VHI and VO are the higher and lower voltage signal amplitude values respectively derived from the two sensors nearest the landing point (and thus with the two highest signal amplitudes), and is an arbitrary constant. When is zero, the ratio factor F is simply the ratio of VHI to VEO, but this makes the value of F very sensitive to variations in VIO. Since VEO is relatively small and may have poor signalto-noise ratio, it is preferable to make some factor below 0.2 which modifies the ratio factor so that its value is smaller and less affected by noise in V[O; this however is at the expense of slightly reducing measurement sensitivity for landing points very close to a sensor.

Figure 8 shows a graph of the ratio factor F plotted against s sensor positions, where the value of has been chosen to give ratio factor values of 5.0 at the peaks corresponding to sensors 12 and 13. (The abscissa values 11, 12, 13 and 14 correspond to the sensors as numbered in Figure 7). Figure 8 is in fact a plot of six separate signals, the graph up to l0 the first minimum corresponding to the case where VI is generated from sensor 11 and VEO is generated from sensor 12.

Similarly, the graph after the last minimum corresponds in the same way to sensors 14 and 13 respectively. These pairs of sensors produce two possible positions where F can have a value of 3 or more and this creates an ambiguity in the measurement. For example, when VHI equals 5.0 near sensors 11 or 14, it is impossible to determine where a landing point is exactly (according to the graph), but the landing point can be recorded as being approximately close to sensor 11 or 14.

The four sections of the graph of Figure 8 between the first and last minima correspond to different pairs of sensors where the sensor that generates VHI has two adjacent sensors on either side, one of which generates VEO. In these circumstances, it is possible to determine the landing position accurately and without ambiguity. It is however necessary to calibrate the relative amplitude versus landing position characteristics for given sensor configurations and ground conditions. For a given value of spacing S. the calibration for one part of the range should be good for any other, so long as the terrain can be considered more or less homogeneous, which is usually the case. If necessary, calibration can be performed wherever sensors are installed.

One means of calibration is to record a large sample of impacts to determine the relationship between landing position and signal amplitude ratios. In a busy driving range, several thousand balls per hour are struck and many of these balls land on targets with sensors as described above.

Provided the spacing S between sensors is small compared to the target distance (i.e. S < D/50 or so) the average distribution of ball-landing positions is uniform, that is, there is equal chance of a ball landing in one position or any another between two adjacent sensors. It then follows that for a ball-impact with ratio factor F. the displacement d of the ball measured from the mid-point between two adjacent sensors is given by: S Nd d =-x- 2 N where Nd is the number of samples with ratio factors equal to or less than F. and N is the total number of samples. This method of calibrating has the advantage that it can be conducted at each target location and can be a continuous process, so that correction can be made for gradual changes in pressure-wave propagation characteristics resulting from seasonal changes in the ground.

In general, the method of estimating landing position as described with reference to Figures 7 and 8 applies to any sensor array involving at least three sensors.

Figure 9 illustrates a target-area of a golf-range, and as typical of many such target-areas is provided with a first set of mutually-parallel piezoelectric-cable sensors 21 that are buried at a substantially-fixed depth (which may be of a few centimetres or as deep as 50 centimetre or more). A second set of mutually-parallel piezoelectric-cable sensors 22 orthogonal to sensors 21 are buried at a different substantially-fixed depth. The difference in depth is of the order of 10 centimetres such that sensors 22 are buried above sensors 21 without danger of disturbing or damaging sensors 21. Both sets of sensors 21 and 22 may be installed using a machine such as a vibrating plough having a cable-laying attachment that automatically guides the cable into a trench formed by the plough. Such equipment is used for installing drainage pipes on golf fairways and the sensors may be laid alongside such pipes. As an alternative, the sensors may be laid manually into trenches and in this case can be laid at the same nominal depth with one set of sensors directly above In the orthogonal set. The sensors run across the length and breadth of the relevant area, and in this respect the two sets could extend throughout substantially the whole of the golf range.

The sensors 21 and 22 in both sets are evenly spaced apart horizontally from one another by a distance S. and are all of a length L as indicated in Figure 9. However, other arrangements and non-parallel distribution may be adopted.

Even with very long sensors 21 and 22, the signal amplitude resulting from a golf-ball landing-impact decreases very severely as the distance of the impact from the sensor increases. Thus, it is preferable, but not a limitation, that the spacing S is less than 5 metre. A ball that travels only a short distance usually has less descent velocity and so generates a landing-impact of smaller intensity, than a ball travelling a long distance. Thus, it is desirable to reduce spacing S in targets close to the tee-off area (i.e. the driving bays) and preferably spacing S should be less than D/50, where D is the distance of the target from the tee-off area.

The sensors 21 and 22 are each connected either at one end or, as shown in Figure 9, at an intermediate point of its length, via inert cables 23 to electronic signal amplification and data-acquisition units 24. The units 24 transmit data to a central computer for analysis and calculation of ball landing times and positions, etc. The splitting of each sensor 21 and 22 near its mid-point as shown in Figure 9 and connection of the twohalves to units 24 doubles the number of sensor channels. This is of especial advantage in the event several balls land nearly simultaneously and adjacent to one of the sensors 21 and 22, but at different positions along its length. It is often difficult in these circumstances to determine correctly the timing and/or position of every ball, especially where the rate of balls landing on the range is high, but by doubling l0 the number of sensor channels, the probability of such signal-conflict is halved. Obviously, each length of sensor 21 and 22 could be divided into three or more smaller sections to reduce further the probability of signal- conflict, but a better solution is to increase the number of IS sensors and reduce the spacing S so as to increase the sensor distribution density.

The receiver units 24 are preferably positioned close to a lightning conductor 25, which may serve as a target-flagpole.

As referred to above in connection with the sensors 1 and 2, the remote end of each sensor 21 and 22 may be terminated by a silicon diode. This enables a forward-biased test to check that the sensors 21 and 22 and/or their inert connecting cables 23 are not open-circuit, and a highimpedance test to check that they are not short-circuit. When not forward biased, the diode is virtually open-circuit and does not degrade the very low-level signals generated in the piezoelectric-cable sensor.

To optimise signal network design, it is preferable to provide sensoramplifiers and data-acquisition electronics proximate to groups of sensors, as described above. However, other arrangements can be provided. For example, all the sensors in an instrumented golf-range may be connected by inert cables to a central signal processing unit, which may be situated near the driving bays. For some applications, it may be necessary to lay sensors across the entire range area and each sensor or sub-section thereof may have a dedicated amplifier and data transmitter that can be poled sequentially from one central data acquisition unit.

The sensors 1 and 2, 11 to 14, and 21 and 22 described above may be typically coaxial in configuration and incorporate a compliant piezoelectric dielectric between an inner core and an outer braiding and may have an inert outer insulating sheath which is tough and durable. Exemplary types of sensor are sold in the UK under the registered trade mark VIBETEK of Ormal Ltd., and use a polyvinylidene fluoride (PVDF) as the compliant piezoelectric dielectric.

Claims

Claims: 1. A method for responding to golf-ball landing-impacts within a

landing area, wherein a plurality of elongate pressure-sensitive sensors are spaced from one another within the landing area, each sensor is responsive along its length to the incidence thereon of a pressure-wave created by impact of a golf ball landing within the area, to provide a signal dependent on the incident wave, and wherein signals provided by the individual sensors in response to a golf-ball impact are analysed to derive therefrom representation of the position of that impact relative to the sensors.
2. A method according to Claim 1 wherein the sensors are elongate piezoelectric cables.
3. A method according to Claim 1 or Claim 2 wherein the sensors extend substantially circumferentially of respective concentric circles within the landing area.
4. A method according to Claim 1 or Claim 2 wherein there are two sets of the sensors, the sensors of each set being mutually parallel and extending orthogonally to the sensors of the other set within the landing area.
5. A method according to any one of Claims 1 to 4 wherein the analysis of the signals is related to the amplitudes of the signals.
6. A method according to Claim 5 wherein the analysis of the signals determines the position of impact as dependent on the relative amplitudes of two signals provided as aforesaid by the sensors in response to that impact.
7. A method according to Claim 6 wherein the analysis of the signals determines the position of impact as dependent on peak-amplitude difference between the two signals.
8. A method according to Claim 6 wherein the analysis of the signals determines the position of impact as dependent on the difference between an average of the peak amplitudes of one of the two signals and a corresponding average of the other signal.
9. A method according to Claim 6 wherein the analysis determines the position of impact as dependent on the difference between root-meansquares of the amplitudes of the two signals.
10. A method according to any one of Claims 5 to 9 wherein the analysis of the signals includes determination of whether a sum of the amplitudes of the two signals exceeds a threshold value and determination of whether a difference between those amplitudes is positive or negative.
11. A method according to any one of Claims 1 to 10 wherein there are more than two said elongate pressure-sensors spaced from one another within the landing area, and the signals provided by all the sensors are compared with one another to select the two of largest amplitude for determining the position of golf-ball impact.
12. A method according to Claim 11 wherein the position of golf-ball impact is determined from a ratio between first and second terms that are dependent respectively on the amplitudes of the two selected, largestamplitude signals.
13. A method according to Claim 12 wherein the first and second terms are also each dependent on the sum of the amplitudes of the two selected, largest-amplitude signals. l
14. A method according to any one of Claims 1 to 13 including a step of calibrating the landing area for the relationship between golf-ball impact position within the landing area and the resulting ratios between the amplitudes of the signals provided by the individual sensors.
15. A system for responding to golf-ball landing- impacts within a landing area, comprising a plurality of elongate pressure-sensitive sensors that are spaced from one another within the landing area, each sensor being responsive along its length to the incidence thereon of a pressure-wave created by impact of a golf ball landing within the area, to provide a signal dependent on the incident wave, and means for analysing the signals provided by the individual sensors in response to a golf-ball impact to derive therefrom representation of the position of that impact relative to the sensors.
16. A system according to Claim 15 wherein the sensors are elongate piezoelectric cables.
17. A system according to Claim 16 wherein the sensor cables are beneath the surface of the landing area.
18. A system according to any one of Claims 15 to 17 wherein the sensors extend substantially circumferentially of respective concentric circles within the landing area.
19. A system according to any one of Claims 15 to 17 wherein there are two sets of the sensors, the sensors of each set being mutually parallel and extending orthogonally to the sensors of the other set within the landing area.
20. A system according to any one of Claims 15 to 19 wherein the analysis of the signals is related to the amplitudes of the signals. 2l
21. A system according to Claim 20 wherein the analysis of the signals determines the position of impact as dependent on the relative amplitudes of two signals provided as aforesaid by the sensors in response to that impact.
22. A system according to Claim 21 wherein the analysis of the signals determines the position of impact as dependent on peak-amplitude difference between the two signals.
23. A system according to Claim 21 wherein the analysis of the signals determines the position of impact as dependent on the difference between an average of the peak voltages of one of the two signals and a corresponding average of the other signal.
24. A system according to Claim 21 wherein the analysis of the signals determines the position of impact as dependent on the difference between root-mean-squares of the amplitudes of the two signals.
25. A system according to any one of Claims 20 to 24 wherein the analysis of the signals includes determination of whether a sum of the amplitudes of the two signals exceeds a threshold value and determination of whether a difference between those amplitudes is positive or negative.
26. A system according to any one of Claims 15 to 25 wherein there are more than two said elongate pressure-sensors spaced from one another within the landing area, and the signals provided by all the sensors are compared with one another to select the two of largest amplitude for determining the position of golf-ball impact.
27. A system according to Claim 26 wherein the position of golf-ball impact is determined from a ratio between first and second terms that are dependent respectively on the amplitudes of the two selected, largestamplitude signals. l
28. A system according to Claim 27 wherein the first and second terms are also each dependent on the sum of the amplitudes of the two selected, largest-amplitude signals.
29. A method for responding to golf-ball landing-impacts within a landing area, substantially as hereinbefore described with reference to the accompanying drawings.
30. A system for responding to golf-ball landing-impacts within a landing area, substantially as hereinbefore described with reference to the accompanying drawings.