A FIFA-compliant match ball from Adidas has a TDK InvenSense 6-axis MotionTracking device and other electronics mounted in the center of the ball. As shown in Figure 1, the Adidas patented suspension system stabilizes the electronics module.
Instead of having the sensing/communication module mounted on the surface of the ball near the inflator valve, the ideal approach is to have it located in the center of the ball. The central location provides the most accurate measurements and does not affect the balance of the ball or the players’ kicking. Also, since the RF communication is in the module, it is important for the module to be separated by a sufficient distance from the ground for the highest signal strength and best possible transmission.
With suspension technology, the sensing/communications module can be safely and securely mounted in the center of the ball. However, regardless of the location, the IMU will feel the impact of the kick. “The suspension system helps the IMU make more accurate, consistent measurements,” says Song Li, Product Marketing Director at TDK InvenSense.
The board is mounted in a pouch, and the pouch is attached to the inside surfaces of the ball using tethers. Ultra-wideband (UWB) technology (typically between 3.1–10.6 GHz) provides time-of-flight measurements for the main position tracking. The IMU delivers more accurate readings including spin, more accurate speed, and more measurement characteristics of the ball. The 3x3x0.9 mm 24-pin QFN packaged accelerometer/gyroscope motion sensor enables real-time ball position tracking. In an official match, this data provides additional information for the Video Assistant Referee (VAR). Having game-ready, FIFA-compliant balls now requires pumping the ball to the proper air pressure and charging the battery in the ball that powers the electronics.
To complete the Semi-Automated Offside Technology (SAOT) system, 12 tracking cameras mounted underneath the roof of stadiums with machine learning track 29 points in players’ bodies.
The first official game to use the combined technology achieved much higher tracking than could be obtained without the IMU. UWB can track 10 cm, and a camera-based system is probably less unless it has a high frame rate camera to capture everything. With the higher frame rate, there is a much higher cost for the overall system, explains Li.
With recorded spin and trajectory provided by the IMU, a coach can do a thorough analysis of each player and each shot to help the player achieve their highest potential. In the replay analysis, the IMU data can fill in the gap that occurs with camera-based analysis. For example, in the 2022 World Cup, one player claimed to have passed the ball (assisted on the goal) when a goal was scored. However, a review of the IMU sensor revealed that the player did not touch the ball. “Without the IMU, it would be hard to figure that out,” says Li.
To perform this level of analysis, it takes a wide-range 3-axis accelerometer that can measure up to a 30-G range as well as a 3D gyroscope with 4000 degrees/second (dps) capability. With measurements sampled at 16-bit resolution, 500 times per second, and system latency of 250 ms, the accelerometer and gyroscope data can be updated in a remarkably short time frame. Part 3 of this three-part blog will explore the sensing capabilities in greater detail.
References
adidas reveals the first FIFA World Cup™ official match ball featuring connected ball technology
Patent US 7,740,551 B2
FIFA will track players’ bodies using AI to make offside calls at 2022 World Cup – The Verge
FIFA’s live ball-tracking technology: How does it work?
