Research On Kinetic Characteristies Of Expressway Hedgerow Pruning Robot

The expressway is not only a part of transportation industry,but also the core of "Belt and Road Initiative" development strategy.Nowadays,the total mileage of expressway in China has reached 131 thousand Km,ranking the first in the world.The hedgerow isolation belt which is used for greening,preventing glare,and ensuring safety,is prevalent in the expressway.In order to achieve a appropriate greening index,regular pruning is required.However,the traditional expressway hedgerow pruning equipment has the problems of low intellectualization,weak pruning stability and poor functional diversity.Therefore,aginst to the above problems,a new expressway hedgerow pruning robot is designed.Then,the positive /inverse kinematics analysing,operation space solving,rigid-flexible coupling dynamic modeling and obstacle avoidance path planning for pruning manipulator are carried out.This topic is derived from the national natural science fund project(project number: 51375519).The main contents of this paper are as follows:(1)According to the greening index of hedgerow isolation belt and the technical requirements of the pruning robot,the overall layout of the hedgerow pruning robot is planned.In view of pruning object,maintaining function and actual situation,the structure of the hedgerow pruning robot is designed.The working mode of driving system and the design requirements of control system are analyzed.The design of driving system and control system is completed,and the experimental prototype is developed.(2)Taking the designed pruning manipulator as research object,the simplified model of the pruning manipulator is established by D-H method.The positive kinematics analysing is carried out,and the position-gesture equation of the end cutters of pruning manipulator is obtained.The inverse kinematics analysing of the pruning manipulator is carried out by inverse transformation method,and the motion expressions of joint angle are derived.Based on Monte Carlo method,the operation space of the manipulator is solved.The numerical simulation of operation space is carried out by MATLAB to verify the correctness of kinematic model and rationality of structure of the pruning manipulator,which provides a theory foundation for the follow-up research of dynamics and obstacle avoidance planning.(3)Based on the theory of multi-body flexible dynamics,the coordinate system of the flexible pruning manipulator is established by floating coordinate method.According to assumed modal method,the elastic deformation of the manipulator is described.Lagrange theory and the principle of virtual work are adopted to derive the rigid-flexible coupling dynamic equations of the pruning manipulator.The dynamic comparison simulation of rigidity and flexibility of the pruning manipulator is carried out by the simulation software ADAMS.The influence of flexible factors on the dynamic characteristics of the system is studied,and the necessity of establishing the rigid-flexible coupling dynamic model is further verified,which provides a theory basis for the future research of precise control and structural optimization.(4)Aiming at the problem of real-time obstacle avoidance for the expressway hedgerow pruning robot manipulator in unstructured environment,a path planning method to avoid obstacle based on perturbed artificial potential field(PAPF)is proposed.According to the distribution of hedgerow and obstacle,the simplified models of obstacle are established.The collision conditions of manipulator and obstacle are analyzed,and then,the collision avoidance space of the manipulator is solved.For the problem such as local minimum point(LMP)and goals nonreachable with obstacle nearby in traditional artificial potential field method,the adjustment strategy and perturbation mechanism of repulsion field are introduced.The path planning simulation of the designed manipulator is carried out in the collision avoidance space by using PAPF.The simulation result shows that the manipulator jumps out of the LMP smoothly and achieves the object point successfully by avoiding obstacle accurately and in real time,which verifies the effectiveness and feasibility of the proposed method.