Posture Synthesis and Control of a Symmetric Hexapod Robot on Corrugated Surfaces for Underwater Observation

This paper presents the first stage of a project to develop a six-legged walker (hexapod) as a highly stable mobile sensor platform for in situ benthic observation. The hexapod is radially symmetric with a downward looking, CCD camera-coupled, microscope mounted co-linear with the central axis of the body. A Lynxmotion (Peoria, IL) Model EH-3R radially symmetric 18 degrees-of-freedom hexapod robot has been used for initial land-based experiments and simplified to a 12 degree-of-freedom structure by locking the panning joint of each leg. Forward and inverse kinematics are then used to derive the relationship between the body posture and the proximal and distal joint angles on legs, which is the basis of the microscope’s coarse focusing for the observation. The kinematics analysis has been verified with both Matlab-based simulations and experiments on the hexapod prototype. Finally, passivity-based posture control is developed and simulated based on the inverse dynamics of the robotic leg.