Research On Motion Trajectory Planning Of Heavy-Load Hydraulic Driven Hexapod Robots

Large hydraulic hexapod robot is a kind of bio-inspired motion machine with high flexibility,reliability,and powerful obstacle surmounting abilities.It can be applied in high-risk or hard-to-reach work environments,such as mining exploration,oil field extraction,landmine detection,and military transportation.It possesses discrete foot placement abilities,all-direction trajectory tracking abilities,and multiple redundant leg and arm operation abilities that wheeled robots do not have.As a cross-product of the fusion of bionics and mechanics,the bio-inspired heavy-duty hydraulic hexapod robot has gradually become an important research field in hexapod robot studies.This article focuses on the path trajectory of the center of mass,the motion trajectory of the foot,and the compensation for trajectory errors of large hydraulic hexapod robots.First,the kinematics of the robot were modeled using the DH parameter method.The mapping model of the displacement,velocity,and force of the hydraulic cylinder and the foot were solved,and the posture mapping model of the body and legs were established.Monte Carlo methods were used to analyze the feasible working range of the robot’s foot end and the distribution of hydraulic cylinder force in space.Based on the operability index,the optimization direction of the leg size was given.Secondly,we proposed a strategy for constructing obstacle grids based on expansion processing and a local path modification scheme considering the robot’s passing ability.An improved ACO and GA fusion-based path generation algorithm was designed for the planar motion trajectory of the body center of mass,and the relationship between the energy consumption index and gait parameters under a fixed path was analyzed.Then,two basic motion representation strategies,oblique and turning,were designed and combined with the planned path trajectory planning to make the hexapod robot capable of all-directional motion planning.Based on bionics,smoothness,and low impact principles,a composite Bezier motion trajectory was designed for the foot,which was extended to three-dimensional space,and the mapping solution of the spatial control points for all-directional foot trajectory planning was completed.After that,a three-dimensional model was created in Solid Works,the motion algorithm was designed in Simulink,the algorithm was transplanted in Gazebo,and the simulation environment was constructed.The motion state was visualized and monitored in RViz,and the simulation verification of the hexapod robot’s all-directional motion planning strategy was completed.Finally,a prediction and compensation method based on extreme learning machine(ELM)was proposed to improve the accuracy of foot trajectory tracking due to the highly nonlinear dynamic behavior of the hydraulic system,such as hydraulic cylinder oil friction,hysteresis,control input saturation,insufficient/overlapping valve opening,and the adverse effects caused by model parameter uncertainty.The effectiveness of the proposed method was verified through experiments.The research in this article provides some technical guidance for the motion planning of hexapod robots.