MR-UBi: Mixed Reality-Based Underwater Robot Arm Teleoperation System With Reaction Torque Indicator via Bilateral Control

Underwater robot-arm teleoperation requires stable grasping, yet operators often struggle to accurately perceive and regulate reaction torque even with bilateral control. To address this issue, we present MR-UBi, a novel mixed reality-based underwater robot-arm teleoperation system with a reaction torque indicator (RTI). The RTI overlays a color- and length-coded torque bar on the MR-HMD, enabling seamless visual–haptic integration. A user study with sixteen participants compared MR-UBi with a bilateral-control baseline. Results show that MR-UBi significantly improves grasping-torque regulation by increasing time within the optimal torque range and reducing under- and over-grasping during lift and pick-and-place tasks with objects of different stiffness. Subjective evaluations further demonstrate higher usability and lower workload. These findings indicate that MR-UBi enables more stable, accurate, and user-friendly underwater robot-arm teleoperation. Video available at: https://mertcookimg.github.io/mr-ubi/.