Design and Open-Water Validation of an Autonomous Underwater Robot for Physical Diver Safety Assistance

Diving accidents remain frequently fatal, and most stem from preventable human factors: panic, failed buoyancy control, and disorientation. Underwater human–robot interaction research has focused on observing the diver and offers little help when a diver must be pulled to safety. This paper presents the design and sea validation of NADIA, an autonomous underwater robot that combines diver guidance and following with diver-commanded physical assistance. A rear handle converts the diver’s grip into thrust and springs back to neutral on release; a diver-facing display shows depth, distance, battery state, and warnings. Six vector thrusters, with mounting angles optimized by gradient descent against drag-model thrust-ratio targets, are driven by an operational-space time-delay controller (TDC-OSF) that keeps the robot in the diver’s view; stereo vision and imaging sonar are fused for diver detection. In test-bed, tank, and sea trials, surge and heave thrusts matched design targets within 5–7%; approval-gated guidance held the robot 1–2 m from the diver with position and heading errors below 0.15 m and 3.5°; and the robot towed a diver at about 1 m/s and rose from 5 m to the surface in about 4 s. An underwater robot can thus serve as a physical safety layer for divers.