Modeling And Simulation Of One-legged Hopping Robot Using Multi-body Dynamics

One-legged hopping robot has a strong ability to adapt to the nonstructuralenvironment and involves research on many basic theories and key technologies, suchas pneumatic servo technology, hydraulic servo technology, self-balancing method forunstable system, and dynamics for multi-degree of freedom system, therefore, researchon one-legged hopping machine is difficult and hot in the field of robotics. Theobjective of this research is to study the kinematics of the mechanism, whose hoppingleg driven by two hydraulic cylinders can rotate relative to the body around thespherical joint, study the dynamics of the one legged hopping robot, lay a basis for theself-balancing method.In order to make the hopping leg move relative to the body in a certain way, themechanism is designed, whose hopping leg and body are connected by a spherical joint,and the hydraulic cylinders are connected with the body at one end and the hopping legat the other end by hook joints and a revolute joint. According to the kinematicscharacteristics of the mechanism whose hopping leg can rotate around the sphericaljoint in three-dimension space, Inverse kinematics equations, by which the extendedlengths of the hydraulic cylinders can be got according to the posture of the hoppingleg relative to the body, are derived. Forward kinematics equations, by which theposture of the hopping leg relative to the body can be got according to the extendedlengths of the hydraulic cylinders, are derived. By analyzing the initial conditions,constraints, force conditions of the robot during buffer stage, dynamics equations forthe piston rod of the pneumatic cylinder, the cylinder of the pneumatic cylinder, thebody, the piston rod of the hydraulic cylinder and the cylinder of the hydraulic cylinderare established, and then the multi-body dynamics model of the one-legged hoppingrobot is got.The kinematics and dynamics simulation model of the robot are built inMATLAB, and then simulation study is done. The simulation results show that theextended lengths of two hydraulic cylinders and the two angles between the hoppingleg and the body form complex surfaces, and the problem of inverse kinematics issolved, making it possible to obtain the extended lengths of two hydraulic cylinders incorrespondence with any posture of the leg relative to the body, the unique forwardkinematics while the leg is driven by the hydraulic cylinders is got by analyzing theconstraints of the structure. Based on dynamics simulation, regularity understandingabout the absolute motion of each part of the robot is got, factors that influence themotion of the robot during buffer stage are analyzed, and necessary basis is providedfor self-balancing method for the one-legged hopping robot.By building three-dimension model in Adams, the relationship between the extended lengths of the hydraulic cylinders and the posture of the leg relative to thebody is verified, and the multi-body dynamics model is also verified, which provethat the simulation results are correct.