Amusement devices: games – Aerial projectile game; game element or accessory therefor... – Target
Patent
1992-12-24
1994-04-19
Grieb, William H.
Amusement devices: games
Aerial projectile game; game element or accessory therefor...
Target
340323R, A63B 6100, A63B 7106
Patent
active
053039157
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a means and method for locating the position of a ball relative to a line on a game surface. In particular the invention relates to a means and method for locating the position of a tennis ball relative to a line on a tennis court.
It will be appreciated that whilst the invention disclosed herein is applicable to the game of tennis it can be applied to other games using lines to mark a playing surface and a ball that can be manufactured with permeable material. It will be understood herein that the term "magnetically permeable" material refer to a material with substantially larger permeability than the magnetic constant (4.pi..times.10.sup.-7 T.m/A). The discussion that follows will refer to the game of tennis as a means to illustrate the invention.
Previous patent specification PCT/AU88/00229 describes an arrangement in which a transmit loop or coil beneath and aligned with the line and is adapted to transmit an alternating magnetic field. A receiver loop or coil is located so that perturbations to the field resulting from magnetically permeable objects moving within the influence of the field are detected by the receiver coil. The receiver coil is connected to detection electronics.
It will be understood herein that a receive coil is connected to a relatively high impedance load. The effect of this is that the receiver coil substantially does not affect the electromagnetic field generated by current flowing through the transmit coil.
Detection electronics described previously consist of input pre-amplifiers connected to the receive coils, synchronous demodulators the reference signals of which are synchronized to the transmit signal and are connected to the said pre-amplifiers, low-pass filters connected to the said synchronous demodulators to remove transmit frequency (carrier) signals and harmonics, processing means connected to the said lowpass filters that apply arithmetic algorithms to the low-pass filter outputs to determine whether the ball is "in" or "out." The tennis ball is manufactured to contain magnetically permeable material such as finely ground iron filings.
The arrangement described in PCT /AU88/00229 typically utilises two synchronous demodulators are connected to each pre-amplifier. The references of each are synchronized to the transmit signal. One with a reference phase selected substantially to pass only reactive signals to its associated low-pass filter. The reference phase of the other said synchronous demodulator being selected so the other said synchronous demodulator substantially pass only resistive signals to its associated low-pass filter. If the magnetic material in the ball is substantially reactive only, magnetically permeable material such as ferrite or fine iron filings, then the "resistive channel" will substantially not pass ball related signals, but will pass noise or resistive signals. Noise or resistive signals can be generated by carbon fibre tennis rackets for example. Thus the resistive channel can be used to determine "interference."
One feature of the system described in PCT /AU88/00229 is that it requires a separate coil system for each straight line. There is a significant problem with this arrangement. The problem is that where the straight lines are intersecting as happens where they form a corner or crossing there will be either interference between the coils or detection becomes ineffective in this location. One reason for this is in the specific way in which the elements are arranged. In the previous example a first coil crossing a second coil can provide an effective shorted turn or effective shorting of one transmit coil by the other. This is because a transmit coil is generally driven by a low impedance source.
This could mean that the coils should be kept from overlaying one another. But this would have the result that an important part of the tennis court line system would not be covered by the ball location detection arrangement. Further, at the end of such non-overlapping coils the arrangement could provide an anomalous
REFERENCES:
patent: 3774194 (1973-11-01), Jokay et al.
patent: 3883860 (1975-05-01), von Kohorn
patent: 4092634 (1978-05-01), von Kohorn
WO 89/00066, Candy, "Ball Location System" Jan. 1989.
WO 83/01904, Gray, "Line Fault Detector", Jun. 1983.
Caldone Pty Limited
Grieb William H.
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