Abstract: Foot-terrain contact impact has a significant effect on the movement performance of large-scale heavy legged robot. A low-impact motion planning method of foot trajectory for hydraulically actuated hexapod robot with the goal of smooth movement is proposed. Angle functions of each joint are deduced based on the bionic configuration and kinematics model, and position control functions of hydraulic cylinder piston rod are solved according to the arrangement of hydraulic cylinder hinged points and the geometric relationship of leg. Analysis results indicate that joints and hydraulic cylinders move steady and their velocity and acceleration are continuous. Simulation platform is established based on Vortex, and simulation of walking process by using the proposed method is completed. The vertical fluctuation of body is tiny in the process of stable moving forward, and the lateral migration rates are about 2.1%. This method is applied to the field experiments of hexapod robot prototype. Test results conclude that the joints move smoothly following the desired trajectory, and the foot force is reasonable. The simulation results and experimental results are consistent, and the rationality and feasibility of the foot trajectory planning method is verified.

Key words: foot trajectory, hydraulic drive, low impact, motion planning, hexapod robot