Research On Swinging-loading Trajectory Planning And Tracking Control Of Hydraulic Excavator

Excavator is an earthmoving engineering machinery that excavates material with a bucket and loads material to transport vehicles or storage piles.It is widely used in mining,municipal construction,rural construction,emergency rescue,and other fields.With the rapid development of modernization in our country,the excavator industry has shown great market potential while facing challenges such as reliance on manual skills,severe aging of drivers,and life safety hazards that urgently need to be addressed.Autonomous operation technology for excavators is the fundamental means to solve these problems.Meanwhile,the rapid development of multidisciplinary fields such as artificial intelligence,electro-hydraulic proportional technology,automatic control field has created favorable conditions for realizing excavator autonomous operation technology.This thesis focuses on the key technologies of hydraulic excavator autonomous operation: the trajectory planning technology and trajectory tracking control technology,in order to improve the working efficiency and precision during the hydraulic excavator swinging-loading stage,which has a significant application prospect.The research contents of this thesis are as follows:(1)Kinematics and dynamics analysis: As the basic content of trajectory planning and trajectory tracking control of swinging-loading,this thesis takes CAT303.5E hydraulic excavator as the prototype to analyze the kinematics and dynamics of hydraulic excavator.Based on the MDH parameter method and geometric method,the kinematics model of hydraulic excavator is established.The kinematics of hydraulic excavator is described in Cartesian space,joint space,and driving space respectively.Thus,the transformation relationship among the tip position of bucket tooth,the angle of each joint,and the extension length of each hydraulic cylinder is obtained.Based on Lagrange method,the mechanical system dynamics model of the hydraulic excavator is established,and the relationship between the rotation angle of each joint and each driving force is obtained.The hydraulic system dynamics model is established,and the relationship between each driving force and each valve opening control signal is obtained.(2)Swinging-loading task analysis and trajectory planning: In the excavator operating cycle,swinging-loading stage takes up a large proportion of time,and trajectory planning for swinging-loading can greatly improve working efficiency.This thesis analyzes the swinging-loading task according to the experience of the driver for flat ground loading.Through the analysis,ideal parking area for the truck relative to the excavator and loading strategy are determined.Taking a single swinging-loading as an example,an improved Bi-RRT path planning algorithm is used to obtain the key path points in the joint space,and the shortest path relative to the key path points is obtained.Based on the seventh-order polynomial interpolation function,trajectory planning is performed for each joint,and the SQP optimization algorithm is used to optimize the existing trajectory with minimum time and minimum jerk as the optimization objectives to obtain the optimal trajectory.(3)Simulation model building and trajectory tracking control: This thesis builds a machine-hydraulic coupling simulation model of hydraulic excavator based on the Simulink/Simscape platform.A cascade control system consisting of an inner loop and an outer loop is adopted to separate the hydraulic system dynamics from the mechanical part,so that the designed controller considers not only the mechanical system dynamics but also the hydraulic system dynamics.The outer loop controller uses PD control based on model compensation,and the inner loop controller uses model-based PID control.To improve the control performance,the outer loop controller introduces a sliding mode switching term and uses the sigmoid function to replace the sign function to solve the system jitter problem.The simulation results demonstrate the superiority of this control system and verify the rationality of the trajectory planned by the swinging-loading trajectory planning method.