Research On Structure Optimization And Walking Characteristics Of Closed-chain Walking Legs Based On Foot Trajectory Optimization Design

At present,the demand for ground mobile robots is increasing year by year,and legged robots are attracting more and more attention due to their strong terrain adaptability.As an important part of the legged robot,the structure of the leg mechanism is mainly based on the open chain and the closed chain.Compared with the open chain mechanism,the closed chain mechanism has the advantages of fewer degrees of freedom,lower control difficulty,and strong carrying capacity.Based on the above considerations,this paper proposes a double-closed-chain leg mechanism composed of "crank slider + crank rocker",and conducts research on its kinematics,foot trajectory planning,dynamics,and motion simulation for different terrains.Finally,the development of a single-legged prototype was completed,and a cycle of foot-end motion trajectory was drawn,laying the foundation for the subsequent design of the closed-chain walking-leg robot.The specific research content includes the following aspects:(1)Based on the double four-bar mechanism of the crank slider and the crank rocker,a two-degree-of-freedom double-crank closed-chain walking leg mechanism driven by continuous full-circle rotation was proposed.Kinematics analysis was carried out,and the foot-end trajectory equation was derived using geometric analysis method,and the mathematical model of closed-chain walking leg mechanism was established.(2)According to the working environment requirements and load-bearing characteristics of the closed-chain walking leg mechanism,an easy-to-calculate and continuously changing foot trajectory curve was planned;and the planned foot trajectory curve was taken as the optimization target,based on the genetic algorithm in the Matlab software,and then Combined with the global search algorithm of the interior point method,optimization calculation was performed to obtain the size of each member in the closed-chain walking leg mechanism.Finally,a single-leg experimental prototype of the closed-chain walking leg mechanism was developed,and a periodic foot trajectory was drawn to verify the correctness of the foot trajectory planning.(3)The dynamic analysis of the whole process of single-leg movement of the closed-chain walking leg mechanism was carried out.Since the closed-chain walking leg mechanism was in motion,the motion forces in the swing phase and the support phase are different,so the dynamic modeling and analysis were carried out at different stages of its motion.For the swing phase,a dynamic model of the swing phase was established,and the related kinematics of the leg mechanism was analyzed.Based on the Lagrangian equation,the closed-chain structure in the closed-chain walking leg was considered,and Lagrange multiplication is introduced.The dynamic equation of the single-leg swing phase was established;and for the support phase,similar to the swing phase,the dynamic equation of the single-leg support phase was established.It provided a theoretical basis for the design and control of the single leg of the closed-chain walking leg mechanism.(4)Carry out the simulation analysis of the walking characteristics of the quadruped robot with the closed-chain walking leg mechanism.According to the closed-chain walking leg mechanism,a virtual prototype model of the quadruped robot was constructed,and the virtual prototypes were respectively simulated for three different road conditions.The walking characteristics of the quadruped robot with the closed-chain walking leg mechanism were studied and analyzed from three angles.