Abstract
Disclosed is system and method for measuring the tension of a tennis net, and, alternatively or in addition, for determining if a service let occurs via the measuring of the net tension. The disclosed embodiments measure a force exerted on the center-strap or the singles stick by the net. In these embodiments, the measured force provides an accurate reflection of the tension of the net.
Claims
1. A net tension system, comprising a net spanning a playing area, wherein the net is supported by a pair of net posts on opposite sides of the playing area; a connector between the net posts, the net connected to the playing area by way of the connector; a scale measuring a force exerted by the net on the connector; and an indicator expressing when a threshold force measured by the scale has been met or exceeded during a short duration using at least one of (1) a vibration force, (2) a light, and (3) a sound, the threshold force being indicative of an impact between a ball and the net.
2. The net tension system as recited in claim 1, wherein the indicator includes a haptic feedback device, and wherein the vibration force is generated by the haptic feedback device.
3. The net tension system as recited in claim 2, wherein the haptic feedback device is incorporated into a handset used by an umpire, official, or other person.
4. The net tension system as recited in claim 1, wherein the indicator includes a light, and wherein the indicator illuminates the light when the threshold force has been met.
5. The net tension system as recited in claim 4, wherein the indicator illuminates the light in a first color when the threshold force has not been met or exceeded, and wherein the indicator illuminates the light in a second color different than the first color when the threshold force has been met.
6. The net tension system as recited in claim 4, wherein the light is incorporated into a base that employs the scale.
7. The net tension system as recited in claim 4, wherein the net is a tennis net, and wherein the light is positioned on or adjacent a center-strap, a net post, or any on-court structure of the playing area.
8. The net tension system as recited in claim 4, wherein the indicator includes a speaker configured to generate the sound when the threshold force has been met or exceeded.
9. The net tension system as recited in claim 1, wherein the indicator includes a speaker configured to generate the sound when the threshold force has been met.
10. The net tension system as recited in claim 1, wherein the threshold force is based on a fingerprint and the fingerprint is a unique sharp spike in an output of the scale during the short duration.
11. A net tension system, comprising a net spanning a playing area, wherein the net is supported by a pair of net posts on opposite sides of the playing area; a connector between the net posts, the net connected to the playing area by way of the connector; a scale measuring a force exerted by the net on the connector; and an indicator expressing when a threshold force measured by the scale has been met or exceeded during a short duration using at least one of an audible signal, a haptic signal, and a visual signal, the threshold force being indicative of an impact between a ball and the net.
12. The net tension system as recited in claim 11, wherein the indicator includes a light, and wherein the signal includes illumination of the light when the threshold force has been met or exceeded.
13. The net tension system as recited in claim 11, wherein the indicator includes a speaker configured to generate the audible signal when the threshold force has been met.
14. The net tension system as recited in claim 11, wherein the threshold force is based on a fingerprint and the fingerprint is a unique sharp spike in an output of the scale during the short duration.
15. A method, comprising: measuring a force exerted by a net on a connector, the net connected to a playing area by way of the connector, the connector provided between a pair of net posts supporting the net on opposite sides of the playing area; and indicating, using an indicator, whether a threshold force has been met or exceeded during a short duration using at least one of (1) a vibration force, (2) a light, and (3) a sound, the threshold force being indicative of an impact between a ball and the net.
16. The method as recited in claim 15, wherein the indicator includes a haptic feedback device, and wherein the indicating step includes generating the vibration force with the haptic feedback device.
17. The method as recited in claim 15, wherein the indicator includes a light, and wherein the indicating step includes illuminating the light after the threshold force has been met or exceeded.
18. The method as recited in claim 17, wherein indicating step includes illuminating the light in a first color when the threshold force has not been met or exceeded and illuminating the light in a second color different than the first color when the threshold force has been met.
19. The method as recited in claim 15, wherein the indicator includes a speaker, and wherein the indicating step includes generating the sound when the threshold force has been met.
20. The method as recited in claim 15, wherein the threshold force is based on a fingerprint, and the fingerprint is a unique sharp spike in an output of a scale during the short duration.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The drawings can be described as follows:
(2) FIG. 1 is a view of an example net tension system.
(3) FIG. 2 is a close-up view of the system of FIG. 1.
(4) FIGS. 3A is a view of another example net tension system.
(5) FIG. 3B is a view of yet another example net tension system.
(6) FIG. 3C illustrate example pull scales for use in the system of FIGS. 1-3A.
(7) FIG. 4 is a view of still another example net tension system.
(8) FIG. 5 is a close-up view of the example net tension system of FIG. 4.
(9) FIGS. 6A-6B show a further example net tension system.
(10) FIG. 7 shows a further example system. In FIG. 7, a light is configured to become illuminated to indicate a let has occurred.
(11) FIG. 8 shows a further example system. In FIG. 8, a speaker is configured to make a relatively loud sound, such as a beep, to indicate a let has occurred.
DETAILED DESCRIPTION
(12) FIG. 1 illustrates an example net tension system 10. The system 10 is used in connection with a net 12, which spans a playing area 14 in a direction of its length L. The playing area 14 in one example is a tennis court, and the net 12 is a tennis net. This disclosure may be used outside of tennis, however.
(13) The net 12 is supported on opposite sides of the playing area 14 by net posts 16 (FIG. 4). The net 12 includes an upper cable 18 (or, net cable) supporting a mesh (or, netting) 20. The upper cable 18 spans the distance between the net posts 16. At least one of the net posts includes a crank (not shown) for adjusting the tension in the upper cable 18. This tension, in turn, tightens the net 12. For all intents and purposes, the term net tension describes the tightness of the net, and is directly related to the tension in the upper cable 18, as well as the force exerted by the net 12 on one or more connectors provided between the net 12 and the playing area 14 (such as the center-strap 22 and the singles stick 43).
(14) The net 12 is connected to the playing surface 14, in this example, by a center-strap 22. The upper cable 18 exerts an upward force F.sub.1 on the center-strap 22 in a direction substantially perpendicular to the length L of the net 12. This is because the net 12 is higher at each end (e.g., the net posts 16 are at 107 cm height) than in the middle, so the center-strap 22 necessarily pulls down upon the net 12, creating the upward force F.sub.1. The center-strap 22 resists the force F.sub.1 with an equal and opposite force to maintain the net 12 in a normal condition (the pre-determined height of the center-strap 22). The force F.sub.1 is resisted by way of the center-strap 22 being connected to the playing surface 14. In one example, the center-strap 22 is connected to the playing surface by a cable 24 attached to a first connecting support 26, which is selectively attachable to a hook 28.
(15) In one example of this disclosure, a scale 30 measures the force F.sub.1 exerted by the upper cable 18 on the center-strap. The force F.sub.1 is indicative of a tension in the net 12. That is, the higher the tension of the upper cable 18, the higher the force F.sub.1 against the center strap 22. As used herein, the term scale refers to any force measuring device, including, but not limited to pull scales 32A-32D (FIG. 3A), compression scales, and load cells (such as tension load cells and tension meters). A system 10 solely for determining net tension would work with a standard scale, while a service let indicator (discussed below) may require a faster load cell to obtain speeds high enough to register a ball strike. In the example where the scale 30 is a load cell, such as an electronic load cell, the system 10 may include an amplifier/digitizer and other associated electronic components. The scale may be digital (as in pull scale 32D), or mechanical (e.g., spring-type, as in pull scales 32A-32C).
(16) As shown in FIG. 2, the scale 30 may be attached to the center-strap 22 by a cable 24, which can be connected to the center-strap 22 via a second connecting support 34. The first connecting support 26 is connected to the playing surface 14 via the hook 28, which is typically built-into tennis courts. If desired, an extension of the center-strap 22 can be attached via the first connecting support 26 to hang downwards and hide the scale 30. Alternatively, the color of the scale 30 may be selected to blend in with the net 12 or playing surface 14. The scale 30 may be connected to the center-strap 22 in other ways.
(17) As illustrated in FIG. 2, the scale 30 may include an indicator 36 expressing the force F.sub.1 measured by the scale 30. In FIG. 2, the indicator 36 includes a digital display 38 that graphically expresses the measured force as a numerical quantity. The indicator 36 of FIG. 2 is attached to the scale 30. In other examples, such as in FIG. 3A, the indicator 36 is provided separately from the scale 30. In FIG. 3A, the indicator 36 may be selectively plugged into the scale 30, via cable 40, to obtain the force measurement. Alternatively, the indicator 36 may be in wireless communication with the scale 30. In one example, the indicator 36 is mounted near a chair umpire or other appropriate official for monitoring during the course of a tennis match. The indicator may include standard buttons, such as power, reset, etc. Because the tension of the net is directly correlated to the height of the net, this will alert the chair umpire (or other official) that, for example, the center-strap 22 has loosened (thus the tension will be lower), allowing the umpire to adjust it at an appropriate time during the match.
(18) While this disclosure extends to all types of indicators 36, the indicator 36 of FIG. 3A may have the advantage of only being used during measurement, and not being exposed and vulnerable to damage during play. The indicator 36 of FIG. 3A further takes up less space, and is not readily visible, compared to that of FIG. 2. Moreover, since there are often several courts in any tennis club or professional tennis tournament, the (potentially) more expensive digital readout of the indicator 36 of FIG. 3A need not be purchased for each and every pull scale 14, since the measuring of the force F.sub.1 can be done on several courts using the same indicator 36.
(19) FIG. 3B shows a variation in which a scale is built into a standard latching found in most tennis center-straps 22. The result is a scale and latching combination that is not appreciably larger than any standard latching. In one example, a pull scale 44 is incorporated into the latching 42. The pull scale 44 may include a spring acting on pin 46, which is connected to the center-strap 22 via the second connecting support 34. The pin 46 is moveable is responsive to the force F.sub.1. The pin 46 is attached to an indicator 48 that moves relative to indicia 50. In one example, the indicia 50 corresponds to a preferred net tension. Other indicia may be present.
(20) FIG. 3C shows three pull scales (e.g., 32A-32C) which are not electronic. While perhaps not as accurate or as easy to read, they have the potential advantage of greater durability, lower cost, and avoid the issue of batteries. These first three scales can be incorporated into this disclosure, should one desire a non-electronic scale. The fourth scale 32D is an example of an off the shelf pocket size digital pull scale.
(21) As the upper cable 18 is adjusted, the force F.sub.1 will change, and, in turn, so will the height H of the net 12 (between the net post 18 or the singles stick 43, and the center-strap 22) and the overall tension in the upper cable 18. In one example, a loose net may indicate a force F.sub.1 of 4.5 kg while a tight net might show a force F.sub.1 of 5.8 kg (approximately 44 N and 57 N, respectively). The scale 30 can accurately measure the force F.sub.1. In the example of FIGS. 1-3B, the measurement is made at a point furthest away from the net posts 16 (e.g., at the center-strap), which may exhibit the least tension, and is also the part of the net 12 most in play. Thus, the force F.sub.1 exerted on the center-strap 22 at this point may provide the most useful information about the overall tension of the net 12.
(22) The measurement can be made with or without singles sticks 43 (FIG. 4), as long as all measurements obtained are consistently. This is, in part, because any change in the angle of a taut upper cable 18 necessarily increases the tension, thus the singles sticks 43 may change the force F.sub.1 on the center-strap 22 (having created a more acute angle), and so measurements with/without the singles stick 43 will be markedly different. Because the placement of the singles sticks 43 must be exact, it may be preferred that the net tension is measured before the singles sticks 43 are placed, thus removing a possible variable. Further, when the upper cable 18 is cranked tighter, it moves slightly laterally and therefore may cause the singles sticks 43 to lose their exact vertical position.
(23) Turning to another embodiment, FIG. 4 illustrates singles sticks 43 provided relative to the net 12. Singles sticks 43 may be used to provide a consistent measurement of the tension of the net 12. In this embodiment, a downward force F.sub.2 from the upper cable 18 of net 12 is measured. It will be understood that the downward force F.sub.2 exerted by the net 12 will vary depending on how far a particular point of measurement is from the net posts 16. A singles stick 43 is, by one example rule, positioned 91.4 cm from the sideline of a singles court. The height H of the net 12 at this point, by example, is 107 cm. As such, because the height and position of the singles stick 43 is precisely defined by the rules of tennis, it can be used to provide a uniform measurement to easily duplicate net tension. The downward force F.sub.2 that the upper cable 18 exerts on the singles sticks 43, in a direction substantially perpendicular to the length L of the net 12, will accurately reflect a tension of the net 12, since the arrangement of the singles stick 43 will be the generally be consistent.
(24) In one example, the singles stick 43 is connected to a scale 52 at its base. Seen in detail in FIG. 5, this scale 52 can be built into the base of the singles stick 43 (as shown), built into the playing surface 14, or be a separate structure. The scale 52 may function substantially as described relative to the scale 30 of FIGS. 1-3B. For instance, the scale 52 may include an indicator 54 having a digital screen 56 for expressing the measured force F.sub.2. This screen 56 can be incorporated into the scale 52 or be separate and attached via a cable when measurements are made.
(25) While there are two singles sticks 43 commonly employed in tennis (one on each end of the net), only one stick is generally required to measure the net tension. Further, it will be appreciated that while a standard singles stick is placed 91.4 cm outside the singles sideline, one can also place the device at another point along the net.
(26) Further, because the presence of the center-strap 22 changes the net tension, the measurements taken at the singles sticks 43 will be markedly different if a center-strap 22 is not used, or if used, not at its regulation 91.4 cm height. Thus, the presence or absence of the center-strap 22 should be noted when measuring the force F.sub.2. Likewise, the presence or absence of the singles sticks 43 should be noted when measuring the force F.sub.1 at the center-strap, as discussed relative to FIGS. 1-3B. This will, again, lead to consistency in the net tension.
(27) FIG. 6A shows a non-digital scale for measuring the force F.sub.2. In FIG. 6A, a singles stick 43 has a first section 58 overlapping a second section 60. The first section 58 is moveable relative to the second section 60. A spring 62 is provided inside the first section 58, and generally resists the force F.sub.2exerted on the singles stick 43 by way of the upper cable 18. Depending on the level of force F.sub.2, the spring 62 will compress a corresponding amount. In turn, the first section 58 will move relative to a second section 62. The first section 58 in this example includes a window 64 and an indicator 66 that slides relative to indicia 68 on the second section 62. Like in the above examples, the indicia 68 may correspond to a preferred net tension.
(28) Turning to FIG. 6B, a U-shaped guide 70 may optionally be attached to the first section 58. The U-shaped guide 70 supports the upper cable 18, and may be adjustable relative to the first section 58 via threads 72. The threads 72 also allow the height of the singles stick 43 to be adjusted to meet the required 107 cm, while also allowing the singles stick 43 to customize the net tension.
(29) Using any of the above embodiments, one can then duplicate a tension time and again. With no measureable variables, that is, the distance between the net posts (12.8 m), the inelasticity of the steel net cable, the height of the single post (107 cm), and the position of the singles stick (91.4 cm outside the single sideline), and the 91.4 cm height of the net at the center-strap, are all fixed by rule, the net tension will substantially be the exact same in each instance. This measurement can be used each time when putting a net up or can be used to simply test periodically that the net tension has remained the same.
(30) An additional benefit of the system 10 relates to the service let rule. A serve that clips the net 12 but still falls in the service box is called a let and is re-played. With the instant disclosure, any ball that comes into contact with the net 12 will change the force (e.g., F.sub.1 or F.sub.2) caused by tension of the net 12. Such a contact and the resulting change in the force will be picked up by the scale. That is, the contact between the ball and the net changes the force F.sub.1, F.sub.2 from a normal level to a threshold level indicating that there has been contact between the net 12 and the ball.
(31) The threshold force will be of an extremely short duration, and may create a unique fingerprint of a sharp spike (dip/peak). When the threshold force is met, an audible signal (beep) may be triggered, indicating a let.
(32) The fingerprint associated with the threshold force will be different than the effect that wind might have. Essentially, the effect of wind on the net tension is more of a constant push than the short-term impact associated with a ball strike. For example, even strong wind gusts have a duration in seconds, while a serve regularly is double or triple that speed, and has an impact duration in milliseconds. Measuring the change of force relative to time (e.g., how fast the force changed from one millisecond to the next one or more) will isolate the signature of a ball impact, allowing it to be identified separately from any wind effect (which will be filtered out). This unique ball strike signature can be used to set the sensitivity for what will be triggered by the threshold force, indicating a let ball.
(33) For purposes of illustrating the point, in the embodiment of FIGS. 1-3B, the force F.sub.1 will be steeply lower during a ball strike (indicating contact as the ball presses the net downward, counteracting (lowering) the force F.sub.1 of the upward pull against the center-strap), while for the singles stick 43, the force F.sub.2 shown after a ball strike will be higher (as the ball slightly presses down on the net). If the change is short enough and strong enough, the threshold force will be reached (indicating a ball strike), thus triggering a beep or signal on the chair umpire device (i.e., the indicator). One example signal includes a vibration in the handset used by the umpire. In this example, the armed button on the handset pressed by the umpire to activate the let detection function for the serve includes a haptic feedback device, such as an asymmetrical rotary device (e.g., an asymmetrical motor), configured to generate a vibration force when the threshold force is reached such that the umpire feels the vibration when a let occurs, just as he might hear a beep. This ensures that the let is noticed by the umpire even in a noisy stadium. Additionally or alternatively, the signal could include a light, such as an LED light turning, for example, from blue to red. The light and vibration may be used in combination with one another and/or in combination with the afore-mentioned beep, providing a redundant three senses signal (audio, haptic, visual) to ensure no let is missed by the umpire. The chair umpire will activate the device only during a serve by pressing a button, which is then released, deactivating it as the point is under way (assuming there is no let or a service fault). At this time, a ball during a rally that clips the net, but lands into play on the other side, are not lets and are not replayed (these are typically called a net cord and play continues since the let rule only relates to serves). Signals indicating a net cord during a rally are neither needed nor desirable since it has no effect on play continuing.
(34) The let indication feature may also be useful in matches, such as club matches or recreational matches, which do not typically involve a chair umpire. FIG. 7 schematically illustrates an embodiment in which an indicator is provided by a light 80. In this example, the light 80 has been incorporated into the scale 30. In one example of use, the light 80 is normally not illuminated during play, and is configured to illuminate when the above-mentioned threshold force is reached. The light 80 may be an LED light configured to illuminate a color that is easily visible by the players, such as red. The red light may stay illuminated for a set period of time, such as 5 seconds, after the let occurs to allow the players to view the light. Thus, when the light is on immediately after a serve, the players know that a let has occurred. If the light, however, comes on during a rally (when play continues even if the ball clips the net cord), the players can ignore the light. Thus, positioning the light 80 on the scale 30, or alternatively in another location, near the bottom of the center-strap 22, for example, helps avoid distracting the players during play.
(35) In another example of use, the light 80 is always illuminated during play in a first color, such as green, which indicates that the above-mentioned threshold force has not been reached. When the threshold force is reached, the color of the light 80 changes to a second color, such as red. If the second color appears immediately following a serve, the players know that a let occurred. If the second color appears during a rally, the players can simply ignore the light.
(36) While only one side of the scale 30 is illustrated in FIG. 7, it should be understood that there may be another light 80 on the opposite side of the scale 30 such that both players can see the light. Alternatively, the light 80 can be positioned on a side of the scale 30 such that it is visible from both sides of a tennis court. Further still, the light 80 could be positioned elsewhere, and need not be incorporated into the scale 30. For example, the light could be positioned below the center-strap 22 or could be positioned off the court in a location easily viewed by both players, such as a net post. Again, since there is no chair umpire or other individual to constantly turn the indicator on and off before a serve, the let detection system of the light 80 may always be activated during play, not just during service. Thus, this disclosure provides the light 80 in a location such that it does not distract the players during a rally, particularly where there is a let cord, but also such that players can easily view the light 80 when desired, such as during service and after a possible let.
(37) FIG. 8 illustrates another example embodiment that is useful in situations where there is no chair umpire. In FIG. 8, the indicator is provided by a speaker 82 configured to make a relatively loud beep when the above-mentioned threshold force is reached. In this example, the speaker 82 is incorporated into the scale 30, but, as with the light 80, that need not be the case. The speaker 82 could be positioned in another location adjacent the tennis court. Both players will be able to hear the beep from the speaker 82, indicating that a let has occurred. The embodiment of FIG. 8 can be used in combination with the embodiment of FIG. 7. That is, a beep could be used in combination with illumination of a light (or a change in color of an already-illuminated light) to indicate that a let has occurred.
(38) It will be appreciated that players could have the ability to activate the let detection function right before a serve, and where the device would automatically de-activate seconds later in order to avoid a possible let signal in a rally. Either or both of the players could activate the device, say, by pressing a button on their person or racket wirelessly connected to the base that activates it right before the serve. While this would require one of the players to remember to activate the device each time before a serve is made, it provides the option of activation of the device only at the time of the serve.
(39) That said, the embodiments of FIGS. 7 and 8 are provided such that the signal, whether audio, visual, or otherwise, will not disturb players during a rally, but the signal could be such that if one player believes that a let occurred, that both players can use the disclosed device to confirm that a let did indeed occur. For example, an example visual signal could be a bright, flashing light, or alternatively could be a discrete light or beep that avoids distracting players but will still provide confirmation if a player calls a let. Thus, since most tennis is not played at the professional level, where chair umpires are always used, this disclosure provides amateur players with a way to enforce an important rule in tennisthe let rule.
(40) Although the different examples have the specific components shown in the illustrations, embodiments of this claimed invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. Furthermore it is appreciated that distances or features in the drawings may be reduced or exaggerated for illustrative purposes and do not in any way so limit the embodiment shown.
(41) For example, while the forces F.sub.1 and F.sub.2 are substantially perpendicular to the length L of the net 12, in an alternate embodiment the scale 30 is arranged to measure the tension in the upper cable 18 directly, although this arrangement may lack sensitivity and responsiveness for the required measurements.
(42) As another example, while specific distances such as 107 cm and 91.4 cm have been mentioned above, as currently required by all tennis governing bodies, it should be understood that this disclosure extends to systems including other distances which may include other sports which employs nets. For instance, if the regulations from the tennis governing bodies are followed, the difference between the height at the net posts 16 and the center-strap 22 will be 15.6 cm. However, in some instances the regulations are not followed, resulting in a height difference of about 15.6 cm. As used herein, the term about is not a boundaryless term, and should be interpreted in the way one skilled in the art would interpret the term. Similarly, measurements as described in the screen readout are given as examples only and will be different under use.
(43) One of ordinary skill in this art would understand that the above-described embodiments are exemplary and non-limiting. That is, modifications of this disclosure would come within the scope of the claims. Accordingly, the following claims should be studied to determine their true scope and content.
