POSITION SENSING

Abstract: Apparatus for detecting the position of an object relative to a plane, comprising at least one energising coil (1) and at least one detecting coil (3, 4), the coils being arranged so that as an object (10) moves relative thereto it affects the detected signal; and phase sensing means for detecting signal variation and indicating the presence or position of the object. The apparatus is arranged so that a detectable phase reversal occurs as the object crosses the plane.

Description: POSITION SENSING This invention relates to position sensing. In particular, it relates to position sensing of balls in sports and to verification of whether a ball has crossed a goal line. The invention has uses in any sport or game in which a goal, point or points are scored when a ball crosses a line, such as football (soccer), rugby, hockey, polo, and so on. The problems of establishing whether a ball has crossed a goal line are well documented. A referee, who has to make the decision, is often badly placed, and may have his or her view obscured, and so cannot tell for certainty whether a goal was scored in a contentious situation. Optical methods have been proposed in which cameras are positioned to view images of the goal area. Again, the fields of view of the cameras can be obscured by players in the goal mouth area and so these systems cannot totally be relied upon. Computer based imaging is possible but also suffers from inaccuracy. The present invention arose in an attempt to provide an improved apparatus for establishing whether a ball has crossed a goal line. According to the present invention there is provided apparatus for detecting whether a goal has been scored, comprising an energising coil disposed between at least two detecting coils, and a ball provided with, or formed of, a material which substantially acts as a shorted electrical winding, whereby, as the ball moves relative to the coils it affects the detected signal, and phase-sensing means for detecting signal variation and indicating the presence or position of the ball, wherein the coils are disposed relative to a goal line such that as the ball crosses the coils the apparatus provides an indication when the ball has crossed the goal line. The arrangement is preferably such that as the ball passes through the relevant line a phase reversal is obtained in the desired signal. Preferably, means are provided to invert or phase-shift the signal from one of the detecting coils relative to at least one other detecting coil. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows schematically a position sensing system; Figure 2 (a)-(d) show the effect of an object moving relative to the system; Figure 3 shows schematically a goal and detecting arrangement; and Figure 4 shows a cross-section through a ball. Figure 1 shows schematically an apparatus comprising a first energising coil 1 which is energised by an AC source 2 at a desired frequency. In one preferred embodiment, the frequency is about 15 kHz, but this frequency may be altered or varied as desired. Two detection coils 3 and 4 are arranged on respective opposing sides of the energising coil 1 and electrical signals are induced in these. Although the coils are shown schematically as having only one turn, they may have a plurality of turns. The signals on the detecting coils are detected by a detection/comparison means 5. Inverting circuitry 6 is also included which serves to phase invert the signals on one of the detecting loops relative to the other one. The detecting/ comparison circuitry then can perform various phase comparisons between the two detected signals from respective loops 3 and 4. It includes a balancing circuit 7 for balancing the detected signals, a phase detection circuit 8 and a microprocessor-based control circuit 9. An amplitude detection measuring circuit 11 may also be included, for indicating that an object is in the vicinity. One or more outputs OPi and OP 2 are connected to visual displays, computerised scoring means, or other indicators (not shown) Although the detecting coils are preferably equispaced on each side of the energising coil 1, this is not necessarily so. It is of course convenient in order to have an equally balanced antiphase relationship between the two, but the antiphase relationship may be generated in many other ways as will be appreciated by those skilled in the art. In use, the coils are positioned around goal posts and/or the goal line (i.e. lying just under the ground) on a sports pitch. The three coils are disposed generally parallel to the goal line. Use of the detecting apparatus will now be described. A ball 10 (e.g. a football) is either made from, or provided with, a material which acts as a shorted electrical winding to affect the signals on the detecting coils. In effect, the coils form a loosely-coupled air-cored transformer and the ball, with the appropriate material, acts as a shorted turn moving around relative to the other coils. Aluminium, or other low resistance material, e.g. phosphor-bronze, may be used, as may many other materials. The object may actually be made of this material or may be treated with it, eg by coating it entirely or partially with the material; by the placing of an insert or small portion of the material either within the product or on its surface; or many other ways. The sensitivity of the detecting system may be arranged so that it is most sensitive to objects of the desired size so that it is relatively insensitive to smaller objects for example. If the object is a football, then the sensitivity may be set appropriately so that articles such as watches or metal boot studs have negligible effect on the apparatus. Since the apparatus functions by a phase relationship, not an amplitude one, it is relatively insensitive to variations in amplitude caused by variation in the separation of the object from the coil wires themselves. When the ball is not in the vicinity of, or at least is not affecting the signals on the coils, then each coil generates a signal which is schematically shown in Figure 2(a) as PI and P2. If PI and P2 are arranged by processing to be in antiphase then a summed signal representing them, shown as Psi is generally flat. As the ball 10 starts to approach one of the RECEIVE coils, it causes an imbalance in the signals PI and P2 due to the changing magnetic geometry of the loosely coupled transformer such that the signal derived from the other coil prevails as shown in Figure 2(b). At this point, the signal derived from coil 3 is less than that from coil 4 and a net signal of a certain phase is produced as Ps 2 . As the object continues on its path, it eventually reaches a position where it equispaced from the two coils shown at Figure 2(c). The effect on the coils is therefore the same and thus a signal Ps 3 is obtained in which the two signals are effectively cancelled out. As soon as the mid-point of the object passes this point, as the object continues on its path, it then begins to cause an imbalance such that a signal in antiphase to that just before the mid-point is detected. That is, the phase reverses as the object crosses the plane. The detecting apparatus senses this phase shift and can provide an appropriate output, eg via output OP1. As the object moves on, signal P s is obtained. The ball itself may be provided with a material such as aluminium or other suitable foil which can be wrapped around an object, perhaps covered by a protective plastics layer for example, without adding significant weight. The material should be a low-impedance material, preferably a flexible skin or membrane. It is preferably applied as an outer layer or a layer sufficiently close to the exterior surface of the ball so that as the surface of the ball is distorted (e.g. by kicking it), so is the layer. The layer may be continuous or may be a mesh or braid for example. It may be an aluminium or phosphor-bronze mesh. In some embodiments, the layer can be formed on a bladder which is inside a ball and is inflated. This is shown in Figure 4 where a 'shorting' mesh 16 is provided on a bladder 15 which is inflated to inflate a ball 10 to its correct pressure. A valve 17 is used, in the normal manner, to inflate the bladder. It will be appreciated that a significant feature of the present invention is that phase differences are used to indicate that a plane has been crossed, irrespective of amplitudes. Thus, the actual spacing of an object from the coils is immaterial since it substantially only effects the amplitude and not the phase of the signal. The system is therefore ideal for situations such as goal posts where a ball may pass anywhere within the rectangle defined by the posts and the ground. Accordingly, in embodiments of the invention, as shown in Figure , the detecting coils 3 and 4 may be placed, respectively, towards the front and rear edges of a goal structure 12 and the energising core will be placed generally between them. As a ball enters the goal, it passes first coil 3 (for example) and then pass coil 4 towards the goal net. When it has just passed the mid-point between coils 3 and 4 a phase shift occurs, and this can be accurately indicated. By placing the coils appropriately, relative to the actual goal line, and arranging for the spacing between coils 3 and 4 to be equal to the diameter of the ball, for example, when the ball passes the plane bisecting them, its trailing part is considered to have just crossed the goal line and therefore a goal is considered to have been scored. According to the current rules of football (soccer) the whole ball must have crossed the goal line for a goal to be scored. The present invention may also be applied advantageously to determining when a ball crosses a goal line in many other sports. Most preferably, amplitude sensing means 11 are included. Since a transformer type coil arrangement is relative prone to noise, etc, spurious indication of objects may arise. These can be avoided by the use of the amplitude detector, which acts as a gating means, or by the use of other gating means. The phase sensing means is only gated to operate when a signal amplitude indicating a desired object in the vicinity is detected. Output OP 2 can be used to indicate the present of an object. Thus, in use, the presence of a ball is indicated by output OP 2 and output OPj indicates whether that ball has passed the goal line (i.e. a pass/fail test). The balancing means 7 equalises the outputs of the two coils and ensures they are in antiphase. The control unit 9 may be arranged to recognise the electrical signature of the ball crossing the line, that is, the change of signal with time as the ball crosses the line, to further aid the discriminating of true from false results. When the apparatus is used around a goal for a football or other game for example, it is of course important that the material of the goal or other body upon which the coils are mounted, is one which does not effect AC fields. It may be non-ferrous (eg wood) and, for example, glued together rather than using screws, nails, etc which could adversely affect fields and will also significantly affect the ease of balancing the output of the coils. Other articles in the vicinity of the goal must also be accounted for. The goal may, for example, be made of glass fibre or similar, with the coils moulded in or attached thereto. Parts of the coil 3 a, 4a, will generally be buried under the ground parallel to the goal line. The parts of the coils mounted on the goal posts 13 and crossbar 14 may be permanently mounted thereon and connected temporarily, e.g. by plug and socket connections 15 when the goal is erected. Alternatively, the coils may be positioned on the goals for each use. The former technique is preferred as the coils can be accurately pre- positioned on the goal and then permanently attached. They could be embedded into the goal structure for example. In some embodiments, the use of more than two energising (or detecting) coils is preferred to improve balancing and/or sensitivity. In some embodiments of the invention, the coils may be self oscillating (ie resonant).

Claims: CLAIMS 1. Apparatus for detecting whether a goal has been scored, comprising an energising ,coil disposed between at least two detecting coils, and a ball provided with, or formed of, a material which substantially behaves as a shorted electrical winding or turn whereby, as the ball moves relative to the coils it affects the detected signal, and phase-sensing means for detecting signal variation and indicating the presence or position of the ball, wherein the coils are disposed relative to a goal line such that as the ball crosses the coils the apparatus provides an indication when the ball has crossed the goal line. 2. Apparatus as claimed in Claim 1, adapted such that as the ball passes across the line, a phase reversal occurs in the detected signal. 3. Apparatus as claimed in Claim 1 or Claim 2, comprising one energising coil mounted between two or more detecting coils. 4. Apparatus as claimed in any preceding claim, including means for inverting or phase shifting the signal from one of the detecting coils or energising coils relative to the other detecting coil or energising coil respectively. 5. Apparatus as claimed in Claim 4, wherein the inverting or phase shifting means produces a phase inversion of one signal relative to the other. 6. Apparatus as claimed in any preceding claim, including gating means for gating the operation of the phase sensing means. 7. Apparatus as claimed in Claim 6, wherein the gating means comprises amplitude sensing means. 8. Apparatus as claimed in any preceding claim, wherein at least part of the coils are disposed on a goal structure and are detachably connected to the plane-sensing means and remaining parts of the coils. 9. Apparatus as claimed in Claim 8, wherein the detachable connection is by a plug and socket means. 10. Apparatus as claimed in any preceding claim, wherein the material is a film, mesh or braid, provided on or in the ball. 11. Apparatus as claimed in Claim 10, wherein the material is disposed so that it distorts as the ball distorts with normal use. 12. Apparatus as claimed in Claim 10 or 11, wherein the material is provided on an internal bladder. 13. Apparatus as claimed in any preceding claim, including means for recognising the electrical signature of the ball as it crosses the goal line. 14. A method of detecting when a ball has crossed a goal line, comprising using an apparatus as claimed in any preceding claim. 15. Apparatus substantially as hereinbefore described, with reference to, and as illustrated by, the accompanying drawings.

Inventors: HUFF DEREK GRAHAM, HUFF, DEREK, GRAHAM
Applicants: HUFF DEREK GRAHAM, INTEGRATED DESIGN LIMITED, HUFF, DEREK, GRAHAM
Application year: 2000
Main classification: A63B63
IPC codes: A63B43, A63B63, A63B71, G01V3