Kinematics And Trajectory Planning Research Of Parallel Leg With Hybrid Chains

With the reduction of traditional energy and the continuous improvement of environmental awareness,nuclear power as a green energy,its demand is increasing.However,whether the exploitation of traditional energy or nuclear power energy,once an accident occurs,it will have a disastrous impact on the staff and the surrounding environment.Therefore,it is of great significance to use robots to inspect and repair equipment in energy development environment.When wheeled and tracked mobile robots are used in unstructured environments,the obstacle-crossing ability is insufficient.The foot robot has the characteristics of discrete foothold and easy adjustment of gravity center,which is suitable for performing emergency inspection tasks in this environment.The motion performance of the foot robot depends largely on the performance of the leg mechanism.At present,the leg mechanism studied by scholars in China and abroad mainly has three forms : series,parallel and hybrid.However,when it is applied to the energy development environment with high temperature,high humidity and strong radiation,there is a widespread problem that the power source is dispersed and it is not convenient for centralized protection.Considering the unstructured environmental adaptability of emergency inspection robots and the protection of power source system,a new type of parallel leg mechanism with hybrid branch is proposed in this paper.The power source is centralized and easy to protect.The degree of freedom analysis,positive and negative solution model,workspace drawing,scale synthesis of key parameters trajectory planning of the new leg mechanism are completed,and the kinematics simulation and single leg swing experiment are carried out.Specific studies are as follows.Firstly,in view of the complex structure of the new parallel leg with hybrid branch,it is divided into drive branch and main branch.Based on the screw theory,the unconstrained characteristics of the drive branch chain are first proved,and then it is proved that the degree of freedom of the hybrid branch parallel leg mechanism is equivalent to the degree of freedom of the main branch,which has three rotations and one movement.The semi-decoupling characteristic of driving branch is proved by the condition of definite motion and spiral analysis of mechanism.Secondly,the forward and inverse kinematics models of the driving space and the joint space are established by coordinate transformation and rod length invariant conditions,respectively.At the same time,the semi-decoupling characteristics of the driving space are verified by the angle of the analytical expression.Based on the general equation of positive solution of position and constraint conditions,the workspace of foot-end point is drawn by using branch chain parameter combination method.With respect to sagittal symmetry,the motion range of each direction basically meets the requirements of movement and obstacle crossing in unstructured environment.Third,the velocity Jacobian matrix is derived based on the position inverse solution equation.Combined with the Jacobian matrix condition number and the characteristics of the separation of driving space and joint space of leg mechanism,an evaluation index of motion performance with weighted mixed condition number is proposed.Taking this index as the objective function,the four key parameters are optimized by the combination of performance spectrum analysis and particle swarm optimization algorithm.Fourth,the foot trajectory is planned based on polynomial curve,and the leg swing motion of leg mechanism is simulated by Adams.First,the leg mechanism is driven by the foot track,then the leg mechanism is driven by the moving pair displacement curve.When the leg swings,it runs smoothly and without impact,which verifies the feasibility of the leg swing.In the end,considering the realization of the kinematic pair and the processing and assembly requirements of each component,the structural details of the new leg mechanism are supplemented and the single leg prototype experimental platform is trial-produced.The motion control program is written based on Zbasic,and then the experiment of single leg swing is carried out,which proves the rationality of the leg mechanism.