Omni-directional sensing and minimum distance calculation using a novel ultrasonic sensor ring system for safe human-robot collaboration

Collision-free Human-Robot Collaboration (HRC) is achieved through accurate monitoring of the human worker's position and the reliable real-time calculation of the minimum separation distance. Herein, we present an innovative ultrasonic-based detection system featuring four strategically positioned sensor rings mounted on robotic arms. Through systematic optimization of ring configuration parameters, including assembly position and tilt angles relative to the primary workspace, the maximal sensing volume coverage while minimizing sensor count is achieved. Furthermore, we present a real-time minimum distance calculation framework using the ultrasonic sensors’ tracking data, to ensure the safety in HRC. In this framework, the robot is represented by capsules and human contours derived from sensor measurements are represented by spheres. A custom calculation algorithm has been developed to overcome the sensor system's misjudgment of the human positioned in front of the robot's end effector, thereby realizing the omni-directional sensing of the human. Finally, the proposed scheme is validated in real experiments using the commercial robot of AUBO-i10. The results demonstrate the system possesses an effectiveness in providing comprehensive human sensing and real-time distance monitoring, establishing a robust solution for safe HRC implementation.