Design and soft-landing control of underwater legged robot for active buffer landing on seabed

Abstract

Traditional underwater vehicles are prone to causing damage to the geomorphology for the close inspection of submarine coral reefs. In this study, a kind of underwater legged robot (ULR) with active buffer landing ability is designed. The kinematics of the robot and the dynamic model considering hydrodynamics are established. To reduce the impact load of the robot landing on the seabed, an active buffer landing control strategy is proposed. The control strategy incorporates state-based impedance parameters adjustment and Spring-loaded Inverted Pendulum (SLIP) model to address the limitations of joint torque and tiptoe force, respectively. The underwater buffer landing process is simulated by the co-simulation of Adams and Matlab/Simulink. When the vertical landing velocity is 1.24 m/s and the negative buoyancy (gravity minus buoyancy) is 25 kgf, the robot can fully absorb the impact energy and reach a stable state within 2.09 s. In addition, the simulation results show that the underwater hexapod robot has the ability to achieve fast and smooth landing under complex conditions. This study provides an important support for the deployment of the underwater legged robot's free diving to the seabed without cable in the future.