GB2621462A

GB2621462A - Tennis let calling system and method using ball flight characteristics

Info

Publication number: GB2621462A
Application number: GB2309669.6A
Authority: GB
Inventors: Goldstein Fredric
Original assignee: GROUP ONE Ltd
Current assignee: GROUP ONE Ltd
Priority date: 2022-06-27
Filing date: 2023-06-27
Publication date: 2024-02-14
Also published as: GB202309669D0; US20230415019A1

Abstract

A method and system comprise, following a serve of a tennis ball, indicating that contact between the tennis ball and a tennis net has occurred when a flight characteristic of the tennis ball changes by a predetermined threshold amount in an area adjacent the tennis net. The system and method may be configured to determine that a net cord let has occurred based on changes ball flight characteristics. The flight characteristics may be determined using a controller in communication with at least one of a camera, radar, infrared light, and a launch monitor. The flight characteristic being determined may be a spin rate, trajectory, velocity, and acceleration of the tennis ball.

Description

TENNIS LET CALLING SYSTEM AND METHOD USING BALL FLIGHT CHARACTERISTICS

This disclosure relates to a let calling system and method, which uses ball flight characteristics to determine whether a let has occurred, as opposed to, for example, monitoring for changes in the net.

This invention relates to a tennis let calling system using ball flight characteristics.

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 a 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. Due to the weight of the net, the cable will have some degree of sag such that there will be an arc between the centerstrap and the net posts or single sticks on either end.

A let is called in tennis only during a serve, which commences all points in tennis. A let is defined as a served ball (i.e., a ball struck during a serve to start a point) making contact with the net as it passes over and continues onwards, subsequently landing on the court surface within the "service box," which are two delineated boxes defined by the painted lines on the court and the net itself Tennis courts have been equipped with let detection systems, which are helpful in determining when a let has occurred, as often lets are not readily perceived by the players or tournament officials, given that the contact between the net and ball may be small and difficult to view with the human eye.

Current let detection systems use sensors to detect the movement of the net caused by the force of the impact of the ball. A drawback of this approach is that factors other than an impact between the ball and the net can cause the net to move, thereby occasionally leading to false positive or false negative indications of a let service. Software is available to address this shortcoming, but the known systems are not foolproof.

A need therefore exists for an improved and or alterative means and/or method for detecting let serves, which the present invention aims to provide. Aspects of the invention are set forth in the appended independent claim or claims. Preferred and/or optional features of the invention are set forth in the appended dependent claims.

In some aspects, the techniques described herein relate to a method, including: following a serve A drawback of a tennis ball, indicating this approach is that contact factors other than an impact between the tennis ball and a tennis net has occurred when a flight characteristic of can cause the tennis ball changes by a predetermined threshold amount in an area adjacent the tennis net.

In some aspects, the techniques described herein relate to move, thereby occasionally leading to a method, wherein the flight characteristic is determined using a controller in communicate with at least one of a camera, radar, infrared light, and a launch monitor.

In some aspects, the techniques described herein relate to a method, wherein the flight characteristic is a spin rate.

In some aspects, the techniques described herein relate to a method, wherein the flight characteristic is one or more of spin rate, trajectory, velocity, and acceleration.

In some aspects, the techniques described herein relate to a method, wherein, following the serve of the tennis ball, the method includes indicating that contact between the tennis ball and the tennis net has occurred when at least two different flight characteristics of the tennis ball change by respective predetermined threshold amounts in the area adjacent the tennis net.

In some aspects, the techniques described herein relate to a method, wherein, following the serve of the tennis ball, the method includes indicating that contact between the tennis ball and the tennis net has occurred when at least three different flight characteristics of the tennis ball change by respective predetermined threshold amounts in the area adjacent the tennis net.

In some aspects, the techniques described herein relate to a method, wherein the area adjacent the tennis net includes a point on a side opposite the side of the tennis net as a server of the tennis ball.

In some aspects, the techniques described herein relate to a method, wherein the area adjacent the tennis net includes a point on a same side of the tennis net as a server of the tennis ball.

In some aspects, the techniques described herein relate to a method, wherein the area adjacent the tennis net includes a point above the tennis net.

In some aspects, the techniques described herein relate to a method, wherein the area adjacent the tennis net includes a point on a side opposite the side of the tennis net as a server of the tennis ball, a point on a same side of the tennis net as a server of the tennis ball, and a point above the tennis net.

In some aspects, the techniques described herein relate to a method, wherein the predetermined threshold amount is a drop of a predefined percentage.

In some aspects, the techniques described herein relate to a method, wherein the predetermined threshold amount is 5%.

In some aspects, the techniques described herein relate to a method, wherein the predetermined threshold amount excludes gradual changes in the flight characteristic.

In some aspects, the techniques described herein relate to a method, wherein the predetermined threshold amount is a fingerprint and is represented as a sudden drop in the flight characteristic.

In some aspects, the techniques described herein relate to a system, including: a sensor configured to generate signals indicative of a flight characteristic of a tennis ball; and a controller configured to interpret signals from the sensor and, based on the signals from the sensor, to indicate that contact between a tennis ball and a tennis net has occurred when the flight characteristic of the tennis ball changes by a predetermined threshold amount in an area adjacent the tennis net.

In some aspects, the techniques described herein relate to a system, wherein the sensor is one of a plurality of sensors in communication with the controller.

In some aspects, the techniques described herein relate to a system, wherein each of the plurality of sensors is a different type of sensor.

In some aspects, the techniques described herein relate to a system, wherein the sensor is one of a camera, radar, infrared light, and a launch monitor.

In some aspects, the techniques described herein relate to a system, wherein the flight characteristic is one or more of spin rate, trajectory, velocity, and acceleration.

In some aspects, the techniques described herein relate to a system, wherein the controller is configured to indicate that contact between the tennis ball and the tennis net has occurred only if at least two different flight characteristics of the tennis ball change by respective predetermined threshold amounts in the area adjacent the tennis net.

Embodiments of the invention shall now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a view of the tennis ball in the instant before it makes contact with the net cord of a tennis net; Figure 2 is a view of the tennis ball in the instant after it makes contact with the net cord of a tennis net; Figure 3 is a perspective view of a tennis court indicating the bulge trajectory of a non-hyphen let serve; Figure 4 is an enlargement of Figure 3 showing the non-let and possible let trajectories of a tennis ball; Figure 5 is an alternative embodiment to that shown in Figure land 2 of the drawings; and Figure 6 is a schematic view of system of Figure 5 in use.

The instant disclosure detects a let by monitoring for changes in the flight characteristics of the tennis ball, as opposed to monitoring for changes in the net.

The velocity of the tennis ball has been measured in real time on tennis courts for decades, for example, using the well-known IBM serve speed screen.

Figure 1 illustrates an example system of this disclosure. In Figure 1, a tennis ball 1 ("ball 1") is shown immediately above a tennis net 2 ("net 2"), which is shown in cross-section.

Figure 1 represents the instant, such as a millisecond or so, prior to initial contact of the ball 1, which may be a served ball, with the net 2. The system includes at least one sensor 3 configured to generate signals indicative of one or more flight characteristics of the ball 1. The system may include one or more of the sensors 3. The sensor 3 may be a camera, radar, infrared light, LiDAR, or a launch monitor, as examples. The sensor 3 may also be a LIDAR (Light Detection and Ranging) sensor or a sensor of a LIDAR system. The system may include multiple sensors of the same type and may alternatively or in addition include one or more sensors of different types. This disclosure is not limited to any particular type of sensor(s), so long as the sensor(s) is/are able to generate signals indicative of one or more flight characteristics of the ball 1. The sensor 3 includes or is in communication with a controller, which may include one or more computing devices, configured to interpret information from the sensor 3 to determine various flight characteristics of the ball 1. In this disclosure, the sensor 3 is aimed at a top of the net 2. If other sensors are present, they may be aimed in other directions. The sensor 3 is configured to generate signals indicative of flight characteristics of the ball 1 immediately before the ball 1 reaches the net 2 in the area adjacent the net, including above or at the net 2 (Figure 1), and at an opposite side of the net 2 (Figure 2) after it has made contact with the net 2. In this way, the system (namely the controller) can determine whether any flight characteristic, such as spin rate, of the ball 1 has dropped by a predetermined threshold amount in the area adjacent the net 2 indicating that contact with the ball 1 and net 2 has occurred and a let should be indicated. A predetermined threshold known to correspond to contact with the ball land the net 2 is predefined and stored in the controller of the system. By defining a predetermined threshold amount, the system reduces the likelihood that environmental factors such as wind gusts will cause the system to erroneously indicate contact between the ball 1 and net 2 has occurred.

While spin rate is mentioned, the system could consider, alternatively or additionally, other flight characteristics such as trajectory, velocity, acceleration (namely deceleration), etc. When those other flight characteristics are considered, the controller is configured to compare the change in those characteristics to other, respective predetermined threshold amounts to determine whether contact between the ball land the net 2 has occurred. The controller may be configured to consider multiple characteristics simultaneously, and may only indicate that contact has occurred if at least two of the monitored characteristics meet or exceed the respective predetermined threshold. Alternatively, the system will indicate contact has occurred when only one characteristic meets or exceeds it corresponding predetermined threshold.

Tennis ball spin rates are currently detectable in modern technology, measuring from point of racket of the serving player to contact to baseline on opposite side of the court by the receiving player. As the serve nearly always involves some degree of top spin, as opposed to backspin by a ground stroke ("slice") during a rally, which is the playing of the point subsequent to the serve. The revolutions of the ball can be tracked by using a fixed point on the ball, e.g., the printed logo, or some other technique.

For the instant disclosure, flight characteristics of a served tennis ball are monitored adjacent the tennis net. In this disclosure, a let will be indicated if there is a sudden, relatively sharp, change in the spin rate, for example, at the specific point over or immediately after the tennis net (i.e., on a side opposite the side of the server). The change may be a drop of a predefined percentage, such as 5%, in the area immediately above or after the tennis net. This anomalous change of rotation at the point the ball travels over the tennis net will indicate contact with the net since the rotation of the ball will necessarily be disrupted by this contact. The amount of change of spin and even the actual spin rate is irrelevant as all served tennis balls will have different spin rates, depending on the skill of the player, wind, etc. As such, in this disclosure, it is the change in flight characteristic that is monitored adjacent the net. Specifically, this disclosure monitors for sudden changes in the flight characteristic to rule out gradual changes from wind gusts or steady deceleration of the tennis ball over time. The sudden change monitored for in this disclosure may be referred to as a fingerprint, and may be represented as a sudden drop in the flight characteristic by a predefined percentage in the area adjacent the net. A graph over time would show a distinct drop in the spin rate at the millisecond the ball passes over the net. Because this is a relative indication, the spin rate is ideally detected a specific duration (or distance) prior to the ball reaching the net, and then detecting any telltale difference as it immediately then passes over the net.

All tennis balls, regardless of the stroke (e.g., rally, volley, serve, etc.) will have various flight characteristics, including velocity, trajectory, and rotation. Rotation is of particular disclosure focus in one aspect of this disclosure, although velocity and trajectory, both separately and together with other flight characteristics, also come within the scope of this disclosure.

A tennis ball typically has a rotational speed of several thousand rotations per minute, depending upon the type of serve the player chooses and if a first or second serve, the latter of which typically have greater spin in lieu of the speed sought in a first serve in order to have greater control to ensure it lands in the service box, and thus not a "double fault." Virtually all aces, defined as serves that the receiver is unable to make contact with, are during the first serves. However, whether first or second serve, the ball will have a high rotation rate. This will typically be "top spin" where the rotation of the ball is in the direction of the forward path of the ball. The rotation is determined by the swing path, speed, and face angle of the tennis racket as it makes contact with the ball during a serve. The ball from a serve will have a trajectory of an arc from the contact point typically from a height of approximately 8ft or more from the court surface at the base line, where serves occur, and maintaining a steady angle moving towards the net as it travels from the baseline to pass over the net, which traverses the width of the court with a height from 91.4cm in the middle to an incremental increase towards 100cm as net height increases closer to the single sticks or net posts, at 107cm, at either end. The rotation rate of the ball is based upon the angle of impact of the tennis racket, the friction of the air (humidity, temperature, altitude, etc), the friction of the ball itself (having a "fuzz" covering its entire surface), and other factors which may also be a constant, such as gravity. This rotation, often reaching 3,000 rpm (rotations per minute) or more will reach its peak almost immediately after leaving the tennis racket and incrementally decrease over time, until it comes in contact with either the net or the court surface. This incremental reduction in rotation will be steady while also affected by the velocity which also incrementally decreases. The "top spin" rotation will affect the ball more as the acceleration of the ball decreases, causing the ball to increase its downward trajectory. The ball travelling at maximum velocity will in turn affect the rotation of the ball but in a predictable steady manner. Similarly, the trajectory of the ball will be affected by the rotation and gravity as the velocity decreases over time.

In the instant disclosure, the measurement of up to three flight characteristics of the ball's travel towards and past the net, namely velocity, trajectory, and/or rotation, can be used to detect any impact of the ball upon the net. An impact by the ball of the net will change all its flight characteristics relatively suddenly. The impact of the net will necessarily reduce the velocity as the forward movement of the ball will in some part be hindered by the net at contact.

The trajectory will change to varying amounts, by the contact with the net cord, which would necessarily interfere with the downward arc of the ball from the contact of the racket from the exact point where the contact occurs. The characteristics of velocity and trajectory can be relatively subtle depending on the degree to which the ball has contacted the net cord. In tennis, any contact of the ball with the net is deemed a "let" and the serve must be done again. The acceleration and trajectory may change to a very small degree, and can be largely masked by gusts of wind coming in any direction.

When considering, however, the rotation of the ball, a relatively freely rotating ball will can exhibit a relatively greater and more perceptible change, at least to the system of this disclosure, upon impact with the net. The rotation of the tennis ball will be disrupted when any object imparts a force upon the ball. The net cord impacts a force upon the ball which is deflected off its prior path, speed, and rotation, since the net cord does not absorb all of the ball's force, otherwise it would not travel over the net to create a let. The impact with the net will however reduce the rpm and, in most cases, will cause the rpm to suddenly drop in excess of a predefined threshold amount that is detectable by

the system of this disclosure.

Modern tennis technology can measure the rotation of all strokes in tennis, such as forehand, backhand, serve, etc. The fact that this disclosure does not measure the ball after it strikes the court surface makes this analysis less complex, given that there are different surfaces in tennis, e.g., hard court, grass, clay, carpet, all of which will greatly affect the rotation and velocity (acceleration) of the ball upon court impact. In an aspect of this disclosure, the system detects flight characteristics at the exact area over the net and then uses that information to determine whether a sudden change, corresponding to a predefined threshold change that indicates contact with the net has occurred, has taken place by comparing the rpm of the ball a predetermined distance prior to the net (on the side of the server) and as it passes immediately over the net to an opposite side of the net from the server. In an aspect of this disclosure, a decrease in spin rate by an amount equal to or greater than the predetermined threshold will indicate contact with the net cord, hence indicate a let has occurred.

For example, as the RPM is steadily reducing over the approximate 12 meters travel from the baseline, where the ball is set in motion, to the net but at the point directly over the net cord has a sudden change, this fingerprint of change can be detected by an appropriate algorithm, and used to indicate contact has occurred (contact with the net being the only possible cause of such a fingerprint change in RPM). Such a system is relatively more immune to the effects of wind on the net since it is motion of the ball that is being measured. While a strong gust of wind can affect the trajectory or velocity of a serve, it has less effect on the rotation of the ball. In other words, while a head wind would necessarily affect the velocity of a ball, this would not be a sudden event as two objects coming into contact with each other. Thus, by measuring the change at the relevant time, this let detection system reliably determines whether an impact between a ball and net has occurred such that a let can or should be indicated. As the ball makes impact with the net, the velocity of the ball results in the amount of time the ball has contact with the net into a millisecond, or even less if the ball barely clips the net cord. Rotation velocity exceeds the velocity of the forward motion of the ball. However, the rotation of the ball will be impeded when it comes into contact with the net, disrupting the relatively free rotation of the ball (apart from air friction, gravity, etc). This disruption of the rate of rotation can be detected by the resulting difference in rotation speed at the relevant time, i.e., when passing over the net.

It is also possible to mesh different metrics of the ball so as to create a broader picture of the ball as it travels over the net. The deceleration of the ball will increase due to impact with the net, and the trajectory may change as well (although more difficult to track such a small change due to the slightest contact of the ball.

Figure 3 of the drawings shows an exemplary tennis court 10 which has a playing surface 12 and a net 14 extending across it. The arrangement of the playing surface 12 and tennis court 10 will be well-known to those of skill in the art.

As previously described, the net 14 is supported by net posts 16 at either side, and a centre strap 18 pulls the middle of the net cord 20 down to create the inverted 'V arrangement. A player (not shown for clarity) serves a ball from the right-hand base line, over the net 14 and into the service box 22 on the other side of the court. The trajectory 24 for a legal serve is shown in Figure 3 by the arrow. It will be seen that the trajectory 24 is straight passing over the net 14 until the ball contacts the service box 22, and then rebounds upwards towards the opposite right base line.

In Figure 4, which is an enlargement of Figure 3 the ball in this case clips the net cord 20 as it passes over the net 14 -a "let serve". As a result of the exchange of energy between the ball and the net 14/ net cord 20, the trajectory of the ball 26, 28 is not the same as it ought to be 24. Using image processing, as has become common place for detecting line faults and the like, deflections away from the non-let trajectory 24 can be interpreted as let serves. In other words, the change in trajectory can be detected by using one or more cameras aimed down the length of the tennis court 10.

Figures Sand 6 the drawings show a slightly different version of the invention shown in Figures land 2. Here, two cameras 3,3a are used and look down the length of the net cord 20 on either side of the net 14. In this example, the ball is being served from right to left and camera 3a captures a sequence of images of the ball 1 before it passes the top of the net 14. By interpolating this series of captured images, it is possible to calculate the trajectory 24 of the ball 1 before is passes over the net 14.

If there is no contact between the ball and the net, then the trajectory 24 ought to be symmetric about a plane of the net 14. In other words, the position of the ball 1 at time delta T ought to be the opposite of the position of the ball at time minus delta T. The expected position of the ball 100 a short time after passing over the net can therefore be calculated by extrapolating the measured trajectory 24. In fact, a permitted envelope 102 of movement of the ball 1 after passing the net can also be calculated.

Referring now to Figure 6, the second camera 3 observes the ball 1 on the opposite side of the net. As can be seen from Figure 6, the bold version Y can be seen in a position that is slightly short of the calculated position 100. This indicates that the ball 1' prime has lost some speed, which is indicative of a contact between the ball and the net. The dash ball 1" is the correct distance past the net but it lies outside the permitted envelope of movement 102, indicating that ball if has been kicked upwardly slightly by the net cord 20 as it passed over the net 14. This is also indicates a let serve.

In a preferred embodiment to the invention, the afore described let calling system using ball flight characteristics are used in conjunction with a conventional net tension or net movement detector. This is particularly useful as it enables both physical and optical methods to be used to detect let serves. A combined arrangement involving both optical and physical monitoring of the ball/net can avoid false positive and false negative let detection indications.

It should be understood that directional terms are used in their normal manner with reference to the game of tennis. Further, these terms have been used herein for purposes of explanation, and should not be considered otherwise limiting. Terms such as "generally," "substantially," and "about" are not intended to be boundaryless terms, and should be interpreted consistent with the way one skilled in the art would interpret those terms.

Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure 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. In addition, the various Figures accompanying this disclosure are not necessarily to scale, and some features may be exaggerated or minimized to show certain details of a particular component or arrangement.

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 10 content.

Claims

CLAIMS1. A method, comprising following a serve of a tennis ball, indicating that contact between the tennis ball and a tennis net has occurred when a flight characteristic of the tennis ball changes by a predetermined threshold amount in an area adjacent the tennis net.
2. The method of claim 1, wherein the flight characteristic is determined using a controller in communicate with at least one of a camera, radar, infrared light, and a launch monitor.
3. The method of claim 1 or claim 2, wherein the flight characteristic is a spin rate.
4. The method of any preceding claim, wherein the flight characteristic is one or more of spin rate, trajectory, velocity, and acceleration.
5. The method of claim 4, wherein, following the serve of the tennis ball, the method includes indicating that contact between the tennis ball and the tennis net has occurred when at least two different flight characteristics of the tennis ball change by respective predetermined threshold amounts in the area adjacent the tennis net.
6. The method of claim 5, wherein, following the serve of the tennis ball, the method includes indicating that contact between the tennis ball and the tennis net has occurred when at least three different flight characteristics of the tennis ball change by respective predetermined threshold amounts in the area adjacent the tennis net.
7. The method of any preceding claim, wherein the area adjacent the tennis net includes a point on a side opposite the side of the tennis net as a server of the tennis ball.
8. The method of any preceding claim, wherein the area adjacent the tennis net includes a point on a same side of the tennis net as a server of the tennis ball.
9. The method of any preceding claim, wherein the area adjacent the tennis net includes a point above the tennis net.
10. The method of any preceding claim, wherein the area adjacent the tennis net includes a point on a side opposite the side of the tennis net as a server of the tennis ball, a point on a same side of the tennis net as a server of the tennis ball, and a point above the tennis net.
11. The method of any preceding claim, wherein the predetermined threshold amount is a drop of a predefined percentage.
12. The method of any preceding claim, wherein the predetermined threshold amount is 5%.
13. The method of any preceding claim, wherein the predetermined threshold amount excludes gradual changes in the flight characteristic.
14. The method of any preceding claim, wherein the predetermined threshold amount is a fingerprint and is represented as a sudden drop in the flight characteristic.
15. A system, comprising: a sensor configured to generate signals indicative of a flight characteristic of a tennis ball; and a controller configured to interpret signals from the sensor and, based on the signals from the sensor, to indicate that contact between a tennis ball and a tennis net has occurred when the flight characteristic of the tennis ball changes by a predetermined threshold amount in an area adjacent the tennis net.
16. The system of claim 15, wherein the sensor is one of a plurality of sensors in communication with the controller.
17. The system of claim 16, wherein each of the plurality of sensors is a different type of sensor.
18. The system of claim 15, 16 or 17, wherein the sensor is one of a camera, radar, infrared light, and a launch monitor.
19. The system of any of claims 15 to 18, wherein the flight characteristic is one or more of spin rate, trajectory, velocity, and acceleration.
20. The system of claim 19, wherein the controller is configured to indicate that contact between the tennis ball and the tennis net has occurred only if at least two different flight characteristics of the tennis ball change by respective predetermined threshold amounts in the area adjacent the tennis net.