Ultrasound-driven Curveball in Table Tennis

Augmented Human (AH) is a research field enhancing human physical abilities or supporting human activity using advanced technologies. As one of the AH approaches, previous studies have attached an actuator to a human body or tools used for an activity. The attached actuators are used to control their movements to support an activity. In this study, instead of attaching actuators, we propose to directly apply noncontact ultrasound force to a lightweight tool to manipulate it. The advantage of using noncontact force is that users do not need to wear a specific device and to process tools used for the activity. As a proof-of-concept system, we developed an ultrasound-based curveball system by which table tennis players can shoot a curveball regardless of their physical ability. In the system, a moving ping-pong ball (PPB) is a target tool for remote manipulation. The system curves the trajectory of a moving PPB by continuously focusing ultrasound on it. Users can control the curve timing and the curve direction (left or right) using a racket-shaped controller. In the user study, we conducted an actual table tennis match using the curveball system and qualitatively confirmed that the player using the system had the upper hand. Another user study using a ball dispenser quantitatively showed that the ultrasound-driven curveball increased the number of mistakes of the opponent player 2.95 times. These results indicate that the proposed concept is feasible.