SYSTEM FOR DETECTING BALL IMPACTS ON TENNIS COURTS AND THE LIKE

Abstract: System for detecting ball impacts on tennis courts and the like, in order to decide whether the ball impact occurred on a line marking or outside thereof. According to the invention, a sound shock collecting device in the form of a resonant box (1) is embedded beneath the court surface. In this resonant box (1), for example, a microphone (2) is located which passes the sound shock in the form of an electric signal to a signal processing unit (6), which screens off electric signals not originating from ball impacts. The signals, were not screened off, and thus originate from a ball impact, are passed to a signal emitting means (8, 9).

Description: System for detecting ball impacts on tennis courts and the like This invention relates to a system of detecting the impacts of balls on tennis courts and the like where it is essential to decide whether the ball impact has occurred on a marking line or outside thereof. Through US-PS 3 415 517 a system for detecting ball impacts on tennis courts is previously known, at which the ball im¬ pact is detected by an impact sensor, which is connected to a signal transducer converting the impact into an output signal. This output signal is controlled in a signal process¬ ing device for deciding whether or not the signal has orig¬ inated from a ball impact. When the signal has been decided having been originated from a ball impact, this signal is converted into an indication, which can be detected by the human senses . . . At this known system the impact sensor is a metallic strip located in or immediately beneath the surface constituting the court and in or beneath the line markings thereof. This system can be employed on such surfaces where the court has a hard surface layer. It. cannot be employed, however, on gravel or lawn courts, because such a strip embedded in or immediately beneath the surface of the court would affect the rebound of a ball meeting the line marking, in or beneath which the sensing strip is laid. The present invention, therefore, has the object to provide a system for detecting ball impacts on tennis courts and the like which can be employed not only on hard surfaces, but also on gravel and lawn courts. This object has been achieved in that the invention has been given the characterizing features defined in the attached claims. The invention is described in greater detail in the follow¬ ing by way of an embodiment thereof exemplified in the acc¬ ompanying drawings, in which Fig. 1 is a block diagram of the system according to the invention, Fig. 2 is a horizontal section through a portion of a res¬ onant box provided with a microphone for use in the system according to the invention, and Fig. 3 is a basic sketch showing how the resonant boxes can be embedded at the sideline markings of a tennis court. The system for detecting ball impacts comprises a plurality of devices 1 for collecting a sound shock from the ball impact. According to the invention, this device 1 consists of a resonant box 1 embedded beneath the tennis court surf¬ ace. In said resonant box, for example in one of its end walls, a microphone.2 , preferably a capacitor microphone with built-in amplifier, is mounted. The sound shock gen¬ erated by the ball impact and collected by the resonant box 1 is converted in the microphone 2 into an electric signal, which via a wire 3 is passed to a selector unit 4, the function of which is to switch-in the microphones in the resonant boxes, which are associated with the line mark¬ ings to be monitored at the occasion in question by the detecting system. From the selector unit 4 the electric signal is passed to an amplifier unit 5 where the signal is amplified. The amplifier unit possibly may be provided with a potentiometer for varying the amplification. After having been amplified in the amplifier unit 5, the signal contin¬ ues to a signal processing unit 6. This unit permits sign¬ als with a certain frequency, viz. such originating from sound shocks caused by ball impacts, to pass, but does not permit the passage of other sound shocks occurring in the resonant box. The signals having passed through the signal processing unit 6 continue to a signal indication selector 7, by which the way can be selected how a ball impact is to be indicated, for example by a signal lamp 8 and/or a head phone or loudspeaker 9. The resonant boxes 1 preferahly are usual box sections of wood or plastic. For outdoor matches box sections of plastic should be used in order to prevent them from being affect¬ ed by moisture in the ground. In one end wall of the resonant box 1 a microphone 2 is inserted, which via a wire 3 is conn¬ ected to the selector unit 4. When the resonant boxes have a very great length, it may possibly be necessary to insert microphones in both end walls of the resonant box. Fig. 3 shows how resonant boxes 1 can be embedded outside the sideline markings 10 and 11 Cfor single and, respective¬ ly, double matches) on a gravel court. The resonance boxes 1 shall be positioned at such a depth beneath the surface that they do not affect the rebound of a ball impacting straight above the embedded boxes 1. In order to prevent a sound shock from a ball rebounding on the sideline marking from being recorded, as an impact outside the line, the resonant box 1 possibly can be provided on its outside or inside with sound and vibration absorbing material, depending on how well the-sound spreads in the court mater¬ ial. The selector unit 4 is arranged so that at different occas¬ ions during the match different sections of the line mark¬ ings on the court can be connected. At service the micro¬ phones in the resonant boxes monitoring the service square in question are connected. Immediately after approved serv¬ ice the microphones in the resonant boxes monitoring the sideline and baseline markings are connected. The signal processing unit 6 comprises a band-pass filter or a frequency decoder, which recognizes the frequency gen¬ erated by a ball impact in the resonant box. It was found at field tests that a great difference in frequency exists between sound shocks from ball impacts and from footsteps. At a resonant box consisting of a PVC-section with cross- sectional dimension 190 x 60 mm, the dominating frequency from a ball impact was about 200 Hz, while the dominating frequency from footsteps was 50-55 Hz. At such great diff¬ erences in frequency between these two most usual sources of sound shocks in the ground of a tennis court, it is, thus, easy to determine the source of sound shocks by means of frequency. / ^ S ξ The present invention has provided the umpire in tennis matches with a reliable and objective auxiliary means for deciding whether a ball has rebound on the line or outside thereof. The signal indication may possibly be connected so as to indicate the court half, in which the ball has been out. The indication also may be arranged so as to be visible to the possible public.

Claims: Claims 1. A system for detecting ball impacts on tennis courts and the like, comprising devices for collecting a sound shock from the ball impact, means for converting sound shocks into an electric signal, a signal processing unit for permitting electric signals within a definite fre¬ quency interval to pass through, and means for emitting a perceptible signal when an electric signal was permitt¬ ed to pass through the signal processing unit, c h a r ¬ a c t e r i z e d i n that the device for collecting the sound shock comprises a resonant box CD embedded beneath the court surface. 2. A system as defined in claim λ s ' c h a r a c t e r ¬ i z e d i n that the resonant box CD is a longit¬ udinal box section of wood or plastic. 3. A system as defined in claim 1 or 2, c h a r a c t e r¬ i z e d i n. that the resonant box CD on at least one side is provided with sound and vibration absorbing material. 4. A system as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the resonant box CD is embedded beneath the court surface so that it is located immediately outside the line marking C10,11) to be monitored by the box. 5. A system as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the means for con¬ verting a sound shock into an electric signal is a capac¬ itor microphone C2) with built-in amplifier. 6. A system as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the signal process¬ ing unit C6) comprises a band-pass filter, which permits the passage of electric signals originating from sound shocks caused by ball impacts. 7. A system as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the means for emitt¬ ing a perceptible signal comprises an indication lamp C8) . 8. A system as defined in claim 7, c h a r a c t e r i z ¬ e d i n that the means for emitting a perceptible signal also comprises a head phone or loudspeaker C9) .

Inventors: BIXO JAN ERIK
Applicants: BIXO JAN ERIK
Application year: 1982
Main classification: A63B71
IPC codes: A63B71