On all tennis courts, perhaps the most notable part is the net. In one known example, a tennis net includes two main net posts placed at a pre-determined height (e.g., 107 cm), and positioned a distance (e.g., 91.4 cm) outside the outermost (or doubles) sidelines of a tennis court. The net is typically composed of a woven or plastic netting supported by an upper net cable. The netting hangs from a strong metal cable via a white net tape. The net cable is attached to one post and then to the opposite post, which has a crank that winds the cable so that the net tightens and rises up to the required height and a desired tension.
In the middle of the net, there is a center-strap (also known as a mid-strap) which holds the net down by coming over the top of the net and being fastened to a clasp on the playing surface. This provides greater tension than a crank could practically provide (by pulling down at the mid-point of the net), since cables generally will sag, and provides the defined low part of the net in the center, and at an determinable height, which is an important during play. The result is a semi-V shape running in the top part of the net, where the center strap provides the regulation 91.4 cm height of the net in the middle.
In many tennis tournaments throughout the world, each net can be different. Wimbledon is known for a loose net while the U.S. Open is known for having a tight highly tensioned net. In fact, because both tournaments are outdoors, the net may be taken down as much as several times on any particular day with inclement weather. From tournament to tournament, and court to court, and even from day to day, and hour to hour, there lacks a precise, uniform net tension in tennis. And with this varying net tension, comes varying net heights (as net height is directly correlated to net tension, as explained further below).
When net tension is different, balls that clip the very top of the net (“net tape”) during a rally will dribble over a loose net (resulting in what is called a cheap point), as a net with a looser tension absorbs the forward movement of the ball, allowing balls which hit the tape to roll over to the other side of the net. Conversely, with a tight net, the ball that clips the net tape will either sit up for an easy put away, or bounce out for a loss of the point, as tighter tensions do not absorb the forward pace and either send balls hitting the tape backward or cause the ball to change trajectory and fly out. This causes inconsistency in playing conditions.
Additionally, as mentioned, when net tension is different, the height of the net will be different. This is despite the fact that the net post is a defined height, as is the center-strap (107 cm and 91.4 cm respectively). The net traverses the court typically at 12.8 m in length (or 10.97 m for a singles net post). The net itself weighs approximately 10 kg (alternately approximately twice that for the ATP World Tour nets). Therefore, there will be a measurable sag in the net even when it is cranked up to reach the center-strap 91.4 cm height. The more one cranks thereafter, the tighter the net, thus as the net tension increases, the sag between the net posts/singles sticks and the center-strap will lessen, as the net cable will straighten out while being pulled tighter (resulting in different heights between those two points). This non-measured cranking (done essentially by “feel”) can result in not only an inconsistent net tension but also an inconsistent net height. While the height of a net is the same for players on both sides, a player with more top spin will have an advantage over a player who hits a flatter ball when the net height can vary as much as several millimeters over the most of the playing area of the net (and as much as 1 cm at the midpoint between the singles stick and center-strap where the sag is greatest). Further, players who prefer to hit down the line (as opposed to cross court) will have a lower/higher net height at precisely that part of the net, with potentially different results of any such shot, depending upon the net tension. As the court itself has strictly defined dimensions and measurements in millimeters, as determined by the tennis governing bodies, and thus define the height of the net at any given point by virtue of knowing (and creating) the net tension.
For serves, the current rules call for a “service let,” which is when the ball clips the net and still falls inside the service box. Loose nets will likely result in more lets while tight nets more likely cause the ball to either bounce back, sit up, or fly further and thus out (a “fault”). Professional tennis had recently considered removing the “service let.” Should this still happen in the future, more “aces” will occur with loose nets (as the ball dribbles over to the other side) while tight nets will cause more balls to sit up for easy winners by the opponent or will go fly out for a loss of the point. The result is different depending upon the net tension. This is unacceptable, as the effect can be different on different courts and even change on the same court on the same day when the net often needs to be taken down on outdoor courts during rain, or to change nets during events with different tours (which have different nets). The result is an ever varying net tension and height for virtually each time a net is set up. This is because the precise height of the net on either side of the centerstrap to each of the net posts (and thus the majority of the playing area) is dependent upon the net tension. Even after the tension is sufficient to pull the centerstrap up to its regulation 91.4 cm (3 ft) height, there remains a sag. Further cranking of the net not only increases the net tension but also straightens up the sag, which raises the net in varying degrees along its length, with the largest increase at the middle of the net between the centerstrap and net posts where most balls pass, and least amount moving closer to either the centerstrap or the net post. At this midpoint, the height differential between a loose net and a tight net can result in up to a centimeter or more discrepancy. Such a difference can have significant effects on play. Therefore, the need to regulate the net tension is more than just how the ball reacts after striking the top of the net cord. It determines the precise height of the net at the most critical parts of the court.
There is a need for consistency in net tension across tennis. 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 tension. The disclosed embodiments measure a force exerted by the net on a center-strap or a singles stick. In these embodiments, the measured force provides an accurate reflection of the tension of the net.
The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to the other embodiments, unless such features are incompatible.
The drawings can be described as follows:
The net 12 is supported on opposite sides of the playing area 14 by net posts 16 (
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 F1 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 F1. The center-strap 22 resists the force F1 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 F1 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.
In one example of this disclosure, a scale 30 measures the force F1 exerted by the upper cable 18 on the center-strap. The force F1 is indicative of a tension in the net 12. That is, the higher the tension of the upper cable 18, the higher the force F1 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 (
As shown in
As illustrated in
While this disclosure extends to all types of indicators 36, the indicator 36 of
As the upper cable 18 is adjusted, the force F1 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 F1 of 4.5 kg while a tight net might show a force F1 of 5.8 kg (approximately 44 N and 57 N, respectively). The scale 30 can accurately measure the force F1. In the example of
The measurement can be made with or without singles sticks 43 (
Turning to another embodiment,
In one example, the singles stick 43 is connected to a scale 52 at its base. Seen in detail in
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.
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 F2. Likewise, the presence or absence of the singles sticks 43 should be noted when measuring the force F1 at the center-strap, as discussed relative to
Turning to
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.
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., F1 or F2) 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 F1, F2 from a normal level to a threshold level indicating that there has been contact between the net 12 and the ball.
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.”
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.
With reference to
As shown in
The handset 92 may include various buttons, including buttons for adjusting settings (e.g., algorithm, beep volume, etc.) and a SET button to enter settings (e.g., algorithm, beep volume, etc.). Further, the tablet 94 may include a software version of the handset 92, and thus the tablet 94 may be used in case of failure of the handset 92. To this end, this disclosure is not limited to use with systems including both a handset 92 and a tablet 94, and extends to systems having one, the other, or both. The handset 92 can be configured to display various information, such as displaying the volume of a beep during a let, for example, and including various LEDs and speakers to indicate, for example, pairing of a remote. The handset 92 and/or the tablet 94 may also show various warning signals, such as loss of wireless connection. In one example, when a wireless signal between the handset 92 and tablet 94 is lost, an LED flashing and “SIGNAL NONE” is displayed on the screen of the handset 92.
The handset 92 and/or tablet 94 may also include a shot clock control button, which can send a signal to selectively start, pause, or resume the shot clock. The “shot clock” indicates on court the 25 second maximum time a player has to serve (i.e., start the next point) after the prior point has ended. As noted above, the handset 92 may also, upon pressing an “ARM” button, which may be an electronic button on a screen of the handset 92 for example, send a signal to the tablet 94 to arm a let detection function and to indicate play has started (i.e., a “Start of Point” signal), which may be sent over the internet around the world.
Specifically, the “ARM” button may be depressed by the umpire 90 during service only, so that the let detection function is armed during service only, meaning lets, per the rules of tennis, are monitored during service only. The “ARM” button is typically deactivated during a rally such that the umpire (or players) is not distracted by notifications indicative of a non-service contact between the ball and net mid-rally. The handset 92 may also send a signal to the tablet 94, using the same button, indicating the next point has started, and which may be used by the tablet 94 to stop/disappear the shot clock from the on-court screen. The handset may manually send the signal to the tablet (using a key sequence) via a button on the handset to start, stop, pause, or resume the 25 seconds time allowed to commence the next point (much like a 30 second shot clock in basketball). The tablet may be connected to the shot clock (cable or wireless) and therefore can control its various functions. The handset may alternatively have a direct connection with the shot clock, wired or wireless, in order to control it. The handset 92 and/or table 94 may also receive signals from a ball mark inspection (“BMI”) remote (not shown), which indicates that the chair umpire 90 has just left his or her chair to perform a ball mark inspection. This may occur during clay court tournaments when the umpire leaves his chair to see the mark a ball makes when it hits the court surface in order to check if the ball is in or out. The tablet 94 may, in turn, send a corresponding signal out to the world that all internet gambling is suspended until the score is input by the umpire 90 upon his or her return to the chair, which prevents chance opportunists on site from placing bets using real time information. This aspect of the disclosure has added relevance in the context of a clay court tournament where the ball makes a visible mark which allows the chair umpire to check a disputed line call. For hard court and grass, typically an automated system, such as the “Electronic Line Calling” is used to determine whether a ball lands inbounds and thus manual court inspection is never performed. The device can automatically reset without any manual intervention by the umpire and be ready for the next ball mark inspection.
Other means of detecting when an umpire chair has left to make a ball mark inspection are publically known, such as a pressure cushion or a so called “dead man's switch” which is a connection (one end to the chair and the other to the chair umpire) that is physically broken when two magnetically connected circuits are separated when the chair umpire leaves his chair. There are distinct disadvantages in such devices.
In one aspect of this disclosure, a separate device, such as a secondary simplified handset, may be paired to a base which houses the scale 30 and configured to display the net tension, in units of force (i.e., Newtons). This separate device may be utilized by a grounds crew as they crank up the net, allowing them to see in real time the precise tension until they reach a target net tension. The target tension may be set at the beginning of the tournament and indicated on the display of the handset to show the preferred net tension. Typically, the handset 92 is only accessible by the chair umpire 90 and not accessible by the grounds crew. Rather than waiting for the umpire to arrive on court and give feedback, the grounds crew can have access to net tension information via the separate device. The separate device may pair to the scale 30, either by a wired or by contact, and preferably operating via wireless connection with the base (the net crank is on one of the two net posts 6.4 m from the middle of the net where the base is). It may be particularly useful by the grounds crew when setting up the net during tournaments where the net will go up and down multiple times a day, thus ensuring the grounds crew can rapidly and safely reach the target net tension as they are operating a crank to apply tension to the net during set up. The separate device reduces, or eliminates, any need for the chair umpire to communicate the net tension to the grounds crew since the grounds crew has access to real time net tension via the separate device. The separate device may also show the battery level of the base, unit number, and other information.
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.
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.
While only one side of the scale 30 is illustrated in
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.
That said, the embodiments of
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.
For example, while the forces F1 and F2 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.
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.
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.
This application is a continuation of U.S. patent application Ser. No. 16/277,095, filed Feb. 15, 2019, which is a continuation of U.S. patent application Ser. No. 16/124,424, filed Sep. 7, 2018, which is a continuation-in-part of prior U.S. application Ser. No. 15/601,721, filed May 22, 2017, which is a continuation-in-part of prior U.S. application Ser. No. 14/646,230, filed May 20, 2015, which is a national stage entry of PCT/US2013/072408, filed Nov. 27, 2013. The '408 PCT Application claims the benefit of U.S. Provisional Application No. 61/730,238, filed Nov. 27, 2012, and U.S. Provisional Application No. 61/737,284, filed Dec. 14, 2012. The entirety of each of these disclosures is herein incorporated by reference.
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