| Hedges are the barriers of orchards,which play a role of separation and protection,making full use of natural resources,maintaining the ecological environment,beautiful and environmentally friendly.However,the trimming of hedges is very tedious.Nowadays,the handheld hedge trimmers are commonly used for trimming,which have large noise,high environmental pollution and low work efficiency.Therefore,the development of efficient automatic trimming manipulator has become a hot spot.In this paper,the automatic hedge trimming manipulator is taken as the research object,and the research is carried out from the structure design,kinematics analysis and trajectory tracking control,which provides theoretical basis for the research and development of intelligent hedge trimming manipulator.The specific research works of the paper are as follows:(1)According to the task requirements of hedge trimming,a four-degree-of-freedom manipulator structure is designed,and the range of motion of each joint is determined.Considering the wheelbase of the carrying vehicle,the distance between the inner wheel and the hedge,and the installation position of the manipulator,etc.,the limit position analysis is carried out to preliminarily determine the length of each link.In addition,the hydraulic drive is used to provide power,and the hydraulic oil circuit is designed.(2)The kinematics of the hydraulic manipulator is analyzed,and the Jacobian matrix is solved.In order to improve the dexterity of the manipulator,taking the global condition index as the objective function,the manipulator structure parameter optimization model is established,and the particle swarm algorithm is utilized to solve this optimization problem to obtain the optimal length of each link.The Monte Carlo method is used to obtain the workspace of the manipulator.The quintic polynomial interpolation function is adopted to plan the trajectory of the manipulator,and the constraint conditions are set to solve the problem according to the given initial position and target position.The kinematics model of the manipulator is established by using Matlab robotic toolbox to verify the correctness of forward and inverse kinematics solution.The motion trajectory of each joint is obtained through simulation,and the obtained angular displacement,angular velocity and angular acceleration curves are smooth and continuous.(3)The coupling dynamics model of the hydraulic manipulator system is established.Lagrange method is used to derive the dynamic equation of the manipulator.The hydraulic oil circuit is analyzed to eastablish the dynamic model of the hydraulic system.In the light of the principle of virtual work,the thrust output of the hydraulic cylinder is converted into the driving torque of each joint,and a more comprehensive coupling dynamics model describing the hydraulic manipulator system is obtained.(4)Aiming at the problem of trajectory tracking control of the hydraulic manipulator with high nonlinearity,complexity and strong disturbance,the control method is studied.Considering that the selection of fuzzy PID controller parameters dependents too much on experience and has the disadvantages of greater subjectivity and blindness,a particle swarm optimization(PSO)algorithm is proposed to optimize the parameters of the controller to improve the control performance of the system.Based on Matlab/Simulink,the control simulation model of the hydraulic manipulator is built.It is verified by simulation that the fuzzy PID controller optimized by PSO can overcome the influence of external disturbance with small tracking error and high trajectory tracking precision. |
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