Leg Mechanism Design And Simulation Analysis For A Heavy-duty Hydraulic Hexapod Robot

Legged Robot is an important branch of mobile robot,and has its own advantages.Compared to wheeled or tracked robot of the same size,legged robot can get a better ability to negotiate obstacles,and to isolate the terrain variations.Moreover,no longer has to continuously overcome ground resistance,legged robot requires less energy when moving on soft ground.As to actuators of legged robots,hydraulic system can supply large force output in a relatively small weight,and has longer endurance due to its various power source.As to the amount of legs,six-legged robots ideally balanced the stability,load capacity and system complexity.In a word,six-legged robot is superior as a field transportation platform under rough terrain or as a recreation facility carrying passengers.This thesis aims at designing the leg mechanism for such a heavy-duty hydraulic six-legged robot with high mobility.After a survey of hydraulic legged robot from all over the world,especially on layout and leg mechanism,a 3-DOF series articulated mechanism was selected,which is a common design for legged robots.The direct and inverse kinematic problem were solved under D-H notation.A brief review on the length ratio of coxa,thigh and shank was revealed,which influences the flexibility of a legged robot.Combined with the design goals of the robot,every link's length has been finally determined.Four scenes,including rapid walking on flat terrain,climbing vertical steps,traveling through longitudinal inclines and lateral inclines,were selected as typical working conditions of the six-legged robot.Gaits have been planned under each condition.A series of simulations were conducted,which showed the robot can walk stably under every working condition.According to the results,contact force between feet and ground was acceptable,and that meant the design goals of the robot were reachable.The contact force was then used as a constraint for leg design.The maximum height of vertical step climbing,the slipping when traveling through inclines and the power consumption were simply discussed based on the simulation results.The relation between require torque and joint angle of base joint,hip joint and knee joint was formed respectively,following the synthesis of all 18 joints' torque requirement.Optimization was conducted to minimize the output force of thigh cylinder and shank cylinder,and another optimization was conducted to minimize the peak flowrate of coxa cylinder.After that,the optimal joint position that meets the torque requirement and other geometry restricts was put forward.Key parameters of cylinders were selected according to the optimization results.A test bench was assembled to test the leg prototype preliminarily.It was observed that the accuracy and speed of cylinders' response were not satisfying,and a more reasonable control method should be applied to the hydraulic proportional system.